Allow completion of partial commands [Powershell]

### Please complete the following tasks

- [X] I have searched the [discussions](https://github.com/clap-rs/clap/discussions)
- [X] I have searched the existing issues

### Clap Version

2.33.3

### Describe your use case

Currently, the completion script generated by clap does not complete partial commands on Powershell (at least on 7.1.4). Examples are from [Starship](https://github.com/starship/starship), which is where I encountered the problem.

No completions are returned when attempting to complete `starship i`  in Powershell:
![image](https://user-images.githubusercontent.com/1317666/131859421-f1ab9b47-7493-442c-873c-3b17277c2c08.png)

But completions are returned when attempting to only complete `starship`:
![image](https://user-images.githubusercontent.com/1317666/131859577-c2dc5884-5188-4cae-88b6-cb9d377898dd.png)

Investigating the completion code, it seems that the `$commandAst` contains the entire string of subcommands as currently entered, which results in the `$command` generated being the string `starship;i` for which there are no completions returned by the completion code, and hence no completions for Powershell to use.

### Describe the solution you'd like

The solution I've managed to put together is to exclude the current `$wordToComplete` from the generated `$command` string, so that the completions for the correct command is being returned. I have only modified the generated completion code for my use, but the relevant code is found in clap/clap_generate/src/generators/shells/powershell.rs, lines 36-38:

```powershell
            if ($element -isnot [StringConstantExpressionAst] -or
                $element.StringConstantType -ne [StringConstantType]::BareWord -or
                $element.Value.StartsWith('-')) {{
```

Changing the condition to:

```powershell
            if ($element -isnot [StringConstantExpressionAst] -or
                $element.StringConstantType -ne [StringConstantType]::BareWord -or
                $element.Value.StartsWith('-') -or
                $element.Value -eq $wordToComplete) {{
```
allows the current word that needs completion to be excluded, and the completions for the correct command to be returned.

### Alternatives, if applicable

_No response_

### Additional Context

Starship's generated completion script is as follows:

```powershell
using namespace System.Management.Automation
using namespace System.Management.Automation.Language

Register-ArgumentCompleter -Native -CommandName 'starship' -ScriptBlock {
    param($wordToComplete, $commandAst, $cursorPosition)

    $commandElements = $commandAst.CommandElements
    $command = @(
        'starship'
        for ($i = 1; $i -lt $commandElements.Count; $i++) {
            $element = $commandElements[$i]
            if ($element -isnot [StringConstantExpressionAst] -or
                $element.StringConstantType -ne [StringConstantType]::BareWord -or
                $element.Value.StartsWith('-')) {
                break
        }
        $element.Value
    }) -join ';'

    $completions = @(switch ($command) {
        'starship' {
            [CompletionResult]::new('-h', 'h', [CompletionResultType]::ParameterName, 'Prints help information')
            [CompletionResult]::new('--help', 'help', [CompletionResultType]::ParameterName, 'Prints help information')
            [CompletionResult]::new('-V', 'V', [CompletionResultType]::ParameterName, 'Prints version information')
            [CompletionResult]::new('--version', 'version', [CompletionResultType]::ParameterName, 'Prints version information')
            [CompletionResult]::new('init', 'init', [CompletionResultType]::ParameterValue, 'Prints the shell function used to execute starship')
            [CompletionResult]::new('prompt', 'prompt', [CompletionResultType]::ParameterValue, 'Prints the full starship prompt')
            [CompletionResult]::new('module', 'module', [CompletionResultType]::ParameterValue, 'Prints a specific prompt module')
            [CompletionResult]::new('config', 'config', [CompletionResultType]::ParameterValue, 'Edit the starship configuration')
            [CompletionResult]::new('print-config', 'print-config', [CompletionResultType]::ParameterValue, 'Prints the computed starship configuration')
            [CompletionResult]::new('toggle', 'toggle', [CompletionResultType]::ParameterValue, 'Toggle a given starship module')
            [CompletionResult]::new('bug-report', 'bug-report', [CompletionResultType]::ParameterValue, 'Create a pre-populated GitHub issue with information about your configuration')
            [CompletionResult]::new('time', 'time', [CompletionResultType]::ParameterValue, 'Prints time in milliseconds')
            [CompletionResult]::new('explain', 'explain', [CompletionResultType]::ParameterValue, 'Explains the currently showing modules')
            [CompletionResult]::new('timings', 'timings', [CompletionResultType]::ParameterValue, 'Prints timings of all active modules')
            [CompletionResult]::new('completions', 'completions', [CompletionResultType]::ParameterValue, 'Generate starship shell completions for your shell to stdout')
            [CompletionResult]::new('session', 'session', [CompletionResultType]::ParameterValue, 'Generate random session key')
            [CompletionResult]::new('help', 'help', [CompletionResultType]::ParameterValue, 'Prints this message or the help of the given subcommand(s)')
            break
        }
        'starship;init' {
            [CompletionResult]::new('--print-full-init', 'print-full-init', [CompletionResultType]::ParameterName, 'Print the main initialization script (as opposed to the init stub)')
            [CompletionResult]::new('-h', 'h', [CompletionResultType]::ParameterName, 'Prints help information')
            [CompletionResult]::new('--help', 'help', [CompletionResultType]::ParameterName, 'Prints help information')
            [CompletionResult]::new('-V', 'V', [CompletionResultType]::ParameterName, 'Prints version information')
            [CompletionResult]::new('--version', 'version', [CompletionResultType]::ParameterName, 'Prints version information')
            break
        }
        'starship;prompt' {
            [CompletionResult]::new('-s', 's', [CompletionResultType]::ParameterName, 'The status code of the previously run command')
            [CompletionResult]::new('--status', 'status', [CompletionResultType]::ParameterName, 'The status code of the previously run command')
            [CompletionResult]::new('--pipestatus', 'pipestatus', [CompletionResultType]::ParameterName, 'Status codes from a command pipeline')
            [CompletionResult]::new('-p', 'p', [CompletionResultType]::ParameterName, 'The path that the prompt should render for.')
            [CompletionResult]::new('--path', 'path', [CompletionResultType]::ParameterName, 'The path that the prompt should render for.')
            [CompletionResult]::new('-P', 'P', [CompletionResultType]::ParameterName, 'The logical path that the prompt should render for. This path should be a virtual/logical representation of the PATH argument.')
            [CompletionResult]::new('--logical-path', 'logical-path', [CompletionResultType]::ParameterName, 'The logical path that the prompt should render for. This path should be a virtual/logical representation of the PATH argument.')
            [CompletionResult]::new('-d', 'd', [CompletionResultType]::ParameterName, 'The execution duration of the last command, in milliseconds')
            [CompletionResult]::new('--cmd-duration', 'cmd-duration', [CompletionResultType]::ParameterName, 'The execution duration of the last command, in milliseconds')
            [CompletionResult]::new('-k', 'k', [CompletionResultType]::ParameterName, 'The keymap of fish/zsh')
            [CompletionResult]::new('--keymap', 'keymap', [CompletionResultType]::ParameterName, 'The keymap of fish/zsh')
            [CompletionResult]::new('-j', 'j', [CompletionResultType]::ParameterName, 'The number of currently running jobs')
            [CompletionResult]::new('--jobs', 'jobs', [CompletionResultType]::ParameterName, 'The number of currently running jobs')
            [CompletionResult]::new('-h', 'h', [CompletionResultType]::ParameterName, 'Prints help information')
            [CompletionResult]::new('--help', 'help', [CompletionResultType]::ParameterName, 'Prints help information')
            [CompletionResult]::new('-V', 'V', [CompletionResultType]::ParameterName, 'Prints version information')
            [CompletionResult]::new('--version', 'version', [CompletionResultType]::ParameterName, 'Prints version information')
            break
        }
        'starship;module' {
            [CompletionResult]::new('-s', 's', [CompletionResultType]::ParameterName, 'The status code of the previously run command')
            [CompletionResult]::new('--status', 'status', [CompletionResultType]::ParameterName, 'The status code of the previously run command')
            [CompletionResult]::new('--pipestatus', 'pipestatus', [CompletionResultType]::ParameterName, 'Status codes from a command pipeline')
            [CompletionResult]::new('-p', 'p', [CompletionResultType]::ParameterName, 'The path that the prompt should render for.')
            [CompletionResult]::new('--path', 'path', [CompletionResultType]::ParameterName, 'The path that the prompt should render for.')
            [CompletionResult]::new('-P', 'P', [CompletionResultType]::ParameterName, 'The logical path that the prompt should render for. This path should be a virtual/logical representation of the PATH argument.')
            [CompletionResult]::new('--logical-path', 'logical-path', [CompletionResultType]::ParameterName, 'The logical path that the prompt should render for. This path should be a virtual/logical representation of the PATH argument.')
            [CompletionResult]::new('-d', 'd', [CompletionResultType]::ParameterName, 'The execution duration of the last command, in milliseconds')
            [CompletionResult]::new('--cmd-duration', 'cmd-duration', [CompletionResultType]::ParameterName, 'The execution duration of the last command, in milliseconds')
            [CompletionResult]::new('-k', 'k', [CompletionResultType]::ParameterName, 'The keymap of fish/zsh')
            [CompletionResult]::new('--keymap', 'keymap', [CompletionResultType]::ParameterName, 'The keymap of fish/zsh')
            [CompletionResult]::new('-j', 'j', [CompletionResultType]::ParameterName, 'The number of currently running jobs')
            [CompletionResult]::new('--jobs', 'jobs', [CompletionResultType]::ParameterName, 'The number of currently running jobs')
            [CompletionResult]::new('-l', 'l', [CompletionResultType]::ParameterName, 'List out all supported modules')
            [CompletionResult]::new('--list', 'list', [CompletionResultType]::ParameterName, 'List out all supported modules')
            [CompletionResult]::new('-h', 'h', [CompletionResultType]::ParameterName, 'Prints help information')
            [CompletionResult]::new('--help', 'help', [CompletionResultType]::ParameterName, 'Prints help information')
            [CompletionResult]::new('-V', 'V', [CompletionResultType]::ParameterName, 'Prints version information')
            [CompletionResult]::new('--version', 'version', [CompletionResultType]::ParameterName, 'Prints version information')
            break
        }
        'starship;config' {
            [CompletionResult]::new('-h', 'h', [CompletionResultType]::ParameterName, 'Prints help information')
            [CompletionResult]::new('--help', 'help', [CompletionResultType]::ParameterName, 'Prints help information')
            [CompletionResult]::new('-V', 'V', [CompletionResultType]::ParameterName, 'Prints version information')
            [CompletionResult]::new('--version', 'version', [CompletionResultType]::ParameterName, 'Prints version information')
            break
        }
        'starship;print-config' {
            [CompletionResult]::new('-d', 'd', [CompletionResultType]::ParameterName, 'Print the default instead of the computed config')
            [CompletionResult]::new('--default', 'default', [CompletionResultType]::ParameterName, 'Print the default instead of the computed config')
            [CompletionResult]::new('-h', 'h', [CompletionResultType]::ParameterName, 'Prints help information')
            [CompletionResult]::new('--help', 'help', [CompletionResultType]::ParameterName, 'Prints help information')
            [CompletionResult]::new('-V', 'V', [CompletionResultType]::ParameterName, 'Prints version information')
            [CompletionResult]::new('--version', 'version', [CompletionResultType]::ParameterName, 'Prints version information')
            break
        }
        'starship;toggle' {
            [CompletionResult]::new('-h', 'h', [CompletionResultType]::ParameterName, 'Prints help information')
            [CompletionResult]::new('--help', 'help', [CompletionResultType]::ParameterName, 'Prints help information')
            [CompletionResult]::new('-V', 'V', [CompletionResultType]::ParameterName, 'Prints version information')
            [CompletionResult]::new('--version', 'version', [CompletionResultType]::ParameterName, 'Prints version information')
            break
        }
        'starship;bug-report' {
            [CompletionResult]::new('-h', 'h', [CompletionResultType]::ParameterName, 'Prints help information')
            [CompletionResult]::new('--help', 'help', [CompletionResultType]::ParameterName, 'Prints help information')
            [CompletionResult]::new('-V', 'V', [CompletionResultType]::ParameterName, 'Prints version information')
            [CompletionResult]::new('--version', 'version', [CompletionResultType]::ParameterName, 'Prints version information')
            break
        }
        'starship;time' {
            [CompletionResult]::new('-h', 'h', [CompletionResultType]::ParameterName, 'Prints help information')
            [CompletionResult]::new('--help', 'help', [CompletionResultType]::ParameterName, 'Prints help information')
            [CompletionResult]::new('-V', 'V', [CompletionResultType]::ParameterName, 'Prints version information')
            [CompletionResult]::new('--version', 'version', [CompletionResultType]::ParameterName, 'Prints version information')
            break
        }
        'starship;explain' {
            [CompletionResult]::new('-h', 'h', [CompletionResultType]::ParameterName, 'Prints help information')
            [CompletionResult]::new('--help', 'help', [CompletionResultType]::ParameterName, 'Prints help information')
            [CompletionResult]::new('-V', 'V', [CompletionResultType]::ParameterName, 'Prints version information')
            [CompletionResult]::new('--version', 'version', [CompletionResultType]::ParameterName, 'Prints version information')
            break
        }
        'starship;timings' {
            [CompletionResult]::new('-h', 'h', [CompletionResultType]::ParameterName, 'Prints help information')
            [CompletionResult]::new('--help', 'help', [CompletionResultType]::ParameterName, 'Prints help information')
            [CompletionResult]::new('-V', 'V', [CompletionResultType]::ParameterName, 'Prints version information')
            [CompletionResult]::new('--version', 'version', [CompletionResultType]::ParameterName, 'Prints version information')
            break
        }
        'starship;completions' {
            [CompletionResult]::new('-h', 'h', [CompletionResultType]::ParameterName, 'Prints help information')
            [CompletionResult]::new('--help', 'help', [CompletionResultType]::ParameterName, 'Prints help information')
            [CompletionResult]::new('-V', 'V', [CompletionResultType]::ParameterName, 'Prints version information')
            [CompletionResult]::new('--version', 'version', [CompletionResultType]::ParameterName, 'Prints version information')
            break
        }
        'starship;session' {
            [CompletionResult]::new('-h', 'h', [CompletionResultType]::ParameterName, 'Prints help information')
            [CompletionResult]::new('--help', 'help', [CompletionResultType]::ParameterName, 'Prints help information')
            [CompletionResult]::new('-V', 'V', [CompletionResultType]::ParameterName, 'Prints version information')
            [CompletionResult]::new('--version', 'version', [CompletionResultType]::ParameterName, 'Prints version information')
            break
        }
        'starship;help' {
            [CompletionResult]::new('-h', 'h', [CompletionResultType]::ParameterName, 'Prints help information')
            [CompletionResult]::new('--help', 'help', [CompletionResultType]::ParameterName, 'Prints help information')
            [CompletionResult]::new('-V', 'V', [CompletionResultType]::ParameterName, 'Prints version information')
            [CompletionResult]::new('--version', 'version', [CompletionResultType]::ParameterName, 'Prints version information')
            break
        }
    })

    $completions.Where{ $_.CompletionText -like "$wordToComplete*" } |
        Sort-Object -Property ListItemText
}
```

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Allow completion of partial commands [Powershell] #2750

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Uh oh!

Allow completion of partial commands [Powershell] #2750

Description

Please complete the following tasks

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Describe your use case

Describe the solution you'd like

Alternatives, if applicable

Additional Context

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Metadata

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Projects

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