The Flutter tool has a bug where removing the last Flutter plugin does not correctly update the CocoaPods integration.
This adds a test to ensure that the generated Swift package is properly updated when the last Flutter plugin is removed.
See: https://github.com/flutter/flutter/issues/11819#issuecomment-2289782626
When Swift Package Manager feature is enabled, create app and create plugin will have Swift Package Manager integration already added and will not need to undergo a migration.
Fixes https://github.com/flutter/flutter/issues/146371.
```
flutter config --enable-swift-package-manager
flutter create --ios-language swift --platforms ios,macos swift_app_name
flutter create --ios-language objc --platforms ios objc_app_name
flutter create --template=plugin --ios-language swift --platforms ios,macos swift_plugin_name
flutter create --template=plugin --ios-language objc --platforms ios objc_plugin_name
```