Prerequisites checklist

• I have read the contributing guidelines.

What is the purpose of this pull request? (put an "X" next to an item)

[x] Documentation update
[ ] Bug fix (template)
[ ] New rule (template)
[ ] Changes an existing rule (template)
[ ] Add autofix to a rule
[ ] Add a CLI option
[ ] Add something to the core
[ ] Other, please explain:

What changes did you make? (Give an overview)

Clarify that the rule meta.deprecated property can be provided as either a boolean or an object.

The current documentation is conflicting:

• https://eslint.org/docs/latest/extend/custom-rules indicates that the property can be a boolean or an object

  deprecated: (boolean | DeprecatedInfo) Indicates whether the rule has been deprecated. You may omit the deprecated property if the rule has not been deprecated.

• https://eslint.org/docs/latest/extend/rule-deprecation implies that the property should only be an object

  In the new format deprecated is an object of type DeprecatedInfo...

The RFC which I started and @DMartens finished shows the property as a boolean or an object:

• feat: additional rule metadata for deprecations rfcs#124

type RuleMeta = {
  deprecated?:
    | boolean // Existing boolean option, backwards compatible.
    | DeprecatedInfo // Proposed extension

My original intention in writing this RFC was that the boolean format would continue to be allowed. In my mind, the DeprecatedInfo object format is only necessary to use when additional information about the deprecation is available. That's why all of the new fields in DeprecatedInfo are optional and can be provided as the rule author sees fit or as additional information is available. Otherwise, simply providing the property as a boolean to indicate the deprecation is totally sufficient.

• Let me know if there's any disagreement about that.

So I've updated the documentation to clarify that boolean or object is acceptable for rule meta.deprecated.

Is there anything you'd like reviewers to focus on?