fix(core): auth Swift support requires FLTFirebaseCorePlugin & messages to be shared

[russellwheatley]

Description

I've been testing this on my own copy of FlutterFire. You can see all iterations of this here: russellwheatley/test-flutterfire@5e6f02c...88b09c9

Changes made

• Moved (symlinked) all firebase core to root Sources/ directory for SPM. Necessary as firebase auth requires FLTFirebaseCorePlugin to be shared which, in turn, requires the last remaining class (and header file) in core which is messages.g.m.
• Created dummy classes for firebase_core as it now has no files (because they are contained within shared firebase core in Sources/) when building on SPM and will throw an exception without any files.
• Updated script for writing txt files in each plugin that has swift support to also update Package.swift file in root with latest firebase_core version and firebase-ios-sdk version.

Unfortunately - swift integration tests won't work until this is merged and release is cut which versions firebase core shared for SPM.

I used the dependency from my own FlutterFire version of this change to use for cloud_firestore example app, and it built successfully:

  example git:(update-core-spm) ✗ flutter run
Resolving dependencies... 
Downloading packages... 
! _flutterfire_internals 1.3.46 from path ../../../_flutterfire_internals (overridden in ./pubspec_overrides.yaml)
  async 2.11.0 (2.12.0 available)
  boolean_selector 2.1.1 (2.1.2 available)
  characters 1.3.0 (1.3.1 available)
  clock 1.1.1 (1.1.2 available)
! cloud_firestore 5.5.0 from path .. (overridden in ./pubspec_overrides.yaml)
! cloud_firestore_platform_interface 6.5.0 from path ../../cloud_firestore_platform_interface (overridden in ./pubspec_overrides.yaml)
! cloud_firestore_web 4.3.4 from path ../../cloud_firestore_web (overridden in ./pubspec_overrides.yaml)
  collection 1.19.0 (1.19.1 available)
  fake_async 1.3.1 (1.3.2 available)
  file 7.0.0 (7.0.1 available)
! firebase_core 3.8.0 from path ../../../firebase_core/firebase_core (overridden in ./pubspec_overrides.yaml)
! firebase_core_platform_interface 5.3.0 from path ../../../firebase_core/firebase_core_platform_interface (overridden in ./pubspec_overrides.yaml)
! firebase_core_web 2.18.1 from path ../../../firebase_core/firebase_core_web (overridden in ./pubspec_overrides.yaml)
  leak_tracker 10.0.7 (10.0.8 available)
  leak_tracker_flutter_testing 3.0.8 (3.0.9 available)
  matcher 0.12.16+1 (0.12.17 available)
  material_color_utilities 0.11.1 (0.12.0 available)
  meta 1.15.0 (1.16.0 available)
  path 1.9.0 (1.9.1 available)
  platform 3.1.5 (3.1.6 available)
  process 5.0.2 (5.0.3 available)
  string_scanner 1.3.0 (1.4.0 available)
  test_api 0.7.3 (0.7.4 available)
  vm_service 14.3.0 (15.0.0 available)
Got dependencies!
18 packages have newer versions incompatible with dependency constraints.
Try `flutter pub outdated` for more information.
Launching lib/main.dart on iPhone 15 in debug mode...
Warning: Missing build name (CFBundleShortVersionString).
Warning: Missing build number (CFBundleVersion).
Action Required: You must set a build name and number in the pubspec.yaml file version field before submitting to the App
Store.
Running Xcode build...                                                  
 └─Compiling, linking and signing...                        11.7s
Xcode build done.                                           53.9s
Syncing files to device iPhone 15...                               103ms

Flutter run key commands.
r Hot reload. 🔥🔥🔥
R Hot restart.
h List all available interactive commands.
d Detach (terminate "flutter run" but leave application running).
c Clear the screen
q Quit (terminate the application on the device).

A Dart VM Service on iPhone 15 is available at: http://127.0.0.1:51001/6xezxRyk0Y8=/
The Flutter DevTools debugger and profiler on iPhone 15 is available at:
http://127.0.0.1:9102?uri=http://127.0.0.1:51001/6xezxRyk0Y8=/

Related Issues

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Checklist

Before you create this PR confirm that it meets all requirements listed below by checking the relevant checkboxes ([x]).
This will ensure a smooth and quick review process. Updating the pubspec.yaml and changelogs is not required.

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• My PR includes unit or integration tests for all changed/updated/fixed behaviors (See Contributor Guide).
• All existing and new tests are passing.
• I updated/added relevant documentation (doc comments with ///).
• The analyzer (melos run analyze) does not report any problems on my PR.
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• I signed the CLA.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• Yes, this is a breaking change.
• No, this is not a breaking change.