Support resolving links in @DeprecationSummary content

[d-ronnqvist]

Bug/issue #, if applicable: rdar://120374614

Summary

This adds support for resolving links in a symbol's @DeprecationSummary content.

Previously the ReferenceResolver didn't visit a symbol's deprecatedSummaryVariants so any link in that content didn't resolve but also didn't warn about the links being unresolved.

Dependencies

None

Testing

In a documentation catalog with any symbol, add documentation extension file with a @DeprecationSummary directive that has a link in its content.

Build and preview the documentation. The deprecation summary should link to the other page.

Replace the link with something that won't resolve—for example ``NotFound``—and rebuild the documentation. There should be a warning about the unresolved link.

Checklist

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

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

[d-ronnqvist]

@swift-ci please test

[d-ronnqvist]

@swift-ci please test

[sofiaromorales]

@d-ronnqvist do you know if there's any reason why @DeprecationSummary is not listed as a directive in the DocC docs? https://www.swift.org/documentation/docc

[d-ronnqvist]

@d-ronnqvist do you know if there's any reason why @DeprecationSummary is not listed as a directive in the DocC docs? https://www.swift.org/documentation/docc

I don't think there's a reason. Why probably my just forgot to list it.

[sofiaromorales]

@d-ronnqvist do you know if there's any reason why @DeprecationSummary is not listed as a directive in the DocC docs? https://www.swift.org/documentation/docc

I don't think there's a reason. Why probably my just forgot to list it.

can we add it as part of this pr?

[d-ronnqvist]

@d-ronnqvist do you know if there's any reason why @DeprecationSummary is not listed as a directive in the DocC docs? https://www.swift.org/documentation/docc

I don't think there's a reason. Why probably my just forgot to list it.

can we add it as part of this pr?

I found that we do intentionally hide it from the documentation but I don't know why.