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
```
