DISCO-2947 - Bump UniFFI to 0.28.0

[bendk]

WIP for now, I want to double check that the CI passes and we also need to get Glean to update.

Pull Request checklist

• Breaking changes: This PR follows our breaking change policy
  • [ ] 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
• [ ] Quality: This PR builds and tests run cleanly
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• [ ] Tests: This PR includes thorough tests or an explanation of why it does not
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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 49.28%. Comparing base (eee6c27) to head (24a9db5).

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #6326       +/-   ##
===========================================
+ Coverage   22.00%   49.28%   +27.28%     
===========================================
  Files         342      146      -196     
  Lines       30712    13713    -16999     
===========================================
  Hits         6759     6759               
+ Misses      23953     6954    -16999     

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[bendk]

I'm hoping to merge this one today, so that we can have a real mozilla/application-services rev for the moz-central patch for this.

I'll wait until https://github.com/mozilla/application-services/pull/6180 has been merged. That way lougenia can vendor in that one without having to worry about the UniFFI upgrade.