Docs: Turn on autodocs for CSF with attached meta.

[tmeasday]

Fixes #20863

Warning
This is a breaking change to Docs 2's naming

What I did

Use the name of the MDX file as the name of the docs entry if not specified. Fall back to docsOptions.defaultName (the autodocs name) only if the file is named the same as the CSF file (e.g. Button.mdx).

How to test

See tests + stories in sandboxes:

Checklist

• Make sure your changes are tested (stories and/or unit, integration, or end-to-end tests)
• Make sure to add/update documentation regarding your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Maintainers

• If this PR should be tested against many or all sandboxes,
  make sure to add the ci:merged or ci:daily GH label to it.
• Make sure this PR contains one of the labels below.

["cleanup", "BREAKING CHANGE", "feature request", "bug", "documentation", "maintenance", "dependencies", "other"]

[JReinhold]

LGTM! I think the failing tests are legit though.