Reset unsupported metadata configuration like the doc comment and diagnostic says

[d-ronnqvist]

Bug/issue #, if applicable: rdar://161219604

Summary

This updates the @Metadata validation for in-source documentation comments to reset unsupported configuration.
This behavior both matches the validation function's documentation comment and the user-facing diagnostic which says that the "configuration will be ignored".

Dependencies

None.

Testing

Add a @TitleHeading, @CallToAction, or @PageImage (inside @Metadata) in an in-source documentation comment for any symbol and build documentation.

• Same as today; The warning that these directives are unsupported in in-source comments continues to be raised.
• New in this PR; these directives are actually ignored and have no effect on the rendered page.

Checklist

Make sure you check off the following items. If they cannot be completed, provide a reason.

• Updated Added tests
• Ran the ./bin/test script and it succeeded
• [ ] Updated documentation if necessary