[api-documenter] Add new showInheritedMembers config for api-documenter and new api-documenter-scenarios test project

[zelliott]

Summary

Fixes #3429. #3469 includes the api-extractor-model changes necessary to support showing an item's inherited members. This PR includes the work in api-documenter to actually show an item's inherited members.

(See zelliott#3 for old PR on fork).

Details

• Adds a new showInheritedMembers api-documenter config (only supported by the MarkdownDocumenter at the moment).
• Creates a new api-documenter-scenarios project.
• Adds a new "inheritedMembers" test scenario that tests this PR as well as [api-extractor-model] Add new ApiItemContainerMixin.findMembersWithInheritance method #3469.
• Significant nit cleanups to the api-documenter project.
• Some nit cleanups to the api-extractor-scenarios project.

How it was tested

Ran rush rebuild and manually inspected generated Markdown artifacts.

[zelliott]

From Zulip:

I'd like some special attention given to the IFindApiItemMessages. I imagine that these messages need to be generic across all "find operations", so I avoided mentioning "inherited members" in any of them.

Is there a way to test these messages? I don't see any code that actually reads IFindApiItemsResult.messages. Maybe the API Documenter test could write it to a file or something? Or maybe at least do a manual test with console.log() to make sure it's printing the display name and not undefined or somesuch.

I added some logic to api-documenter that logs out the messages and manually inspected that they made sense. They all made sense except surprisingly the ExtendsClassLikeVariable declaration in the api-documenter-scenarios test case reported a DeclarationResolutionFailed message instead of an UnsupportedKind message. This is because the canonical reference for ClassLikeVariable is incorrect, causing declaration resolution to fail (feel free to take a look at the .api.json). So all WAI at the end of the day.

[octogonz]

Before merging, we'll test this by regenerating the Rush Stack API reference.

[octogonz]

Here's the branch that I tested with:

microsoft/rushstack-websites@767d2a7...octogonz/api-docs-test

The output is deployed to the live site: https://api.rushstack.io/pages/

Example of a class with inherited members: https://api.rushstack.io/pages/ts-command-line.commandlineparser/