af: Add symlinks to ios and macos [SDK-4693]

[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 symlinks all the files within the darwin directory into the ios and macos directories. This is necessary because pub does not support symlinking directories, so each file has to be symlinked individually.

The .gitignore file inside darwin was copied instead of symlinked, because of Git behavior:

Commits:

• 4139430 adds the symlinks to the ios directory
• a2091c2 adds the symlinks to the macos directory

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

❗ No coverage uploaded for pull request base (feature/macos-support@b2370e5). Click here to learn what that means.

Additional details and impacted files

@@                   Coverage Diff                    @@
##             feature/macos-support     #350   +/-   ##
========================================================
  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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