Add CI job to check iOS/macOS symlinks [SDK-4714] 1/2

[Widcket]

• All new/changed/fixed functionality is covered by tests (or N/A)
• I have added documentation for all new/changed functionality (or N/A)

📋 Changes

This PR ensures the iOS/macOS symlinks are always in sync with the contents of the darwin directory, by adding a new CI job that:

1. Regenerates the iOS/macOS symlinks
2. Uses Git to check if there were any changes

If there are changes, the CI job fails and prints a message informing how to fix the problem. If there are no changes, that means the symlinks are in sync, so the job succeeds.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

❗ No coverage uploaded for pull request base (feature/macos-support@844e03c). Click here to learn what that means.

Additional details and impacted files

@@                   Coverage Diff                    @@
##             feature/macos-support     #352   +/-   ##
========================================================
  Coverage                         ?   96.36%           
========================================================
  Files                            ?       98           
  Lines                            ?     1596           
  Branches                         ?      328           
========================================================
  Hits                             ?     1538           
  Misses                           ?       50           
  Partials                         ?        8           

Flag	Coverage Δ
auth0_flutter	100.00% <0.00%> (?)
auth0_flutter_android	97.35% <0.00%> (?)
auth0_flutter_ios	99.85% <0.00%> (?)
auth0_flutter_platform_interface	87.03% <0.00%> (?)

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