Bug Description:

There are issues when using the vscode.git and vscode.git-ui builtins as it references unsupported menu paths:

Failed to register a menu item for plugin vscode.git contributed to scm/sourceControl

Failed to register a menu item for plugin vscode.git contributed to editor/content

Failed to register a menu item for plugin vscode.git contributed to scm/change/title

Steps to Reproduce:

1. remove vscode.git and vscode.git-ui from the exclusion list

3. remove @theia/git and @theia/scm-extra from the example applications
4. rebuild, and confirm that the download:script pulls the git builtins
5. notice the errors related to not being able to set the toolbar items