[various] Add Swift Package Manager integration to example apps (#8219)
This migrates various example apps to have Swift Package Manager integration. This raises the example apps' Flutter SDK requirement to 3.24.0 or higher.
I will get a text exemption for this change.
The example apps were migrated using the following commands:
```
dart run script/tool/bin/flutter_plugin_tools.dart build-examples --ios --swift-package-manager
dart run script/tool/bin/flutter_plugin_tools.dart build-examples --macos --swift-package-manager
```
â ï¸ The following plugins' example apps are **not* included in this change as their migration included non-SPM changes that require closer review:
1. google_sign_in
1. google_sign_in_ios
1. image_picker
1. image_picker_ios
1. image_picker_macos
1. pigeon
Part of: https://github.com/flutter/flutter/issues/159173
[various] Migrate example apps' AppDelegate.swift (#8155)
Migrated by running:
```
dart run script/tool/bin/flutter_plugin_tools.dart build-examples --ios --swift-package-manager
dart run script/tool/bin/flutter_plugin_tools.dart build-examples --macos --swift-package-manager
```
Tests aren't updated as this change should not affect semantics. I will get a test exemption.
Part of https://github.com/flutter/flutter/issues/159173
Remove use_modular_headers! from Podfiles (#7796)
â ï¸ _This PR does not update packages' versions as it only affects unpublished parts of example apps and tests._
We added use_modular_headers! to our Podfiles as we originally planned to phase out use_frameworks! (see https://github.com/flutter/flutter/pull/42204). However, our plans have now changed and we are instead phasing out CocoaPods entirely in favor of Swift Package Manager.
CocoaPods's use_frameworks! and use_modular_headers! are two different overlapping options that should not be used together. This change removes the use_modular_headers! from example apps' Podfiles. This change does not affect packages themselves.
Part of https://github.com/flutter/flutter/issues/156259