DocC doesn't warn when a documentation file doesn't match a symbol

[d-ronnqvist]

Description

When the symbol link in a documentation file doesn't match a symbol the content of that documentation file isn't used in the build and there's no diagnostic to inform the developer of this issue.

Checklist

• If possible, I've reproduced the issue using the main branch of this package.
• This issue hasn't been addressed in an existing GitHub issue.

Expected Behavior

There should be a similar diagnostic for this as there are for other unresolved symbol links, but specific to the context of documentation extensions and more specific about this impact.

Actual behavior

No response

Steps To Reproduce

In a Swift package with a documentation catalog, add a documentation file and write an symbol link in the header that doesn't exist in the project:

# ``MyModule/ThisDoesNotExist

This content won't appear in the documentation

Swift-DocC Version Information

e135c5b

Swift Compiler Version Information

swift-driver version: 1.80.1 Apple Swift version 5.9 (swiftlang-5.9.0.108.11 clang-1500.0.19.2)
Target: x86_64-apple-macosx13.0

[d-ronnqvist]

This could be a decent first issue but at the same time I may want to fix it sooner than later. I'll add the tag but I'll probably start working on this next week.

[d-ronnqvist]

The work I'm doing for #561 also addresses this issue so I'm removing the "good first issue" label