Switch relevancy component from UDL to proc-macros [ci full]

[gruberb]

Pull Request checklist

• Breaking changes: This PR follows our breaking change policy
  • [x] This PR follows the breaking change policy:
    • This PR has no breaking API changes, or
    • There are corresponding PRs for our consumer applications that resolve the breaking changes and have been approved
• [x] Quality: This PR builds and tests run cleanly
  • Note:
    • For changes that need extra cross-platform testing, consider adding [ci full] to the PR title.
    • If this pull request includes a breaking change, consider cutting a new release after merging.
• [ ] Tests: This PR includes thorough tests or an explanation of why it does not
• [ ] Changelog: This PR includes a changelog entry in CHANGELOG.md or an explanation of why it does not need one
  • Any breaking changes to Swift or Kotlin binding APIs are noted explicitly
• [ ] Dependencies: This PR follows our dependency management guidelines
  • Any new dependencies are accompanied by a summary of the due diligence applied in selecting them.

Branch builds: add [firefox-android: branch-name] to the PR title.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 50.15%. Comparing base (8be45cd) to head (1ea32e0).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6327      +/-   ##
==========================================
+ Coverage   49.30%   50.15%   +0.85%     
==========================================
  Files         146      139       -7     
  Lines       13708    13475     -233     
==========================================
  Hits         6759     6759              
+ Misses       6949     6716     -233     

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