Use case

Just like having a AppDelegate that subclass from FlutterAppDelegate, we should have a SceneDelegate that subclass from FlutterSceneDelegate in our new app template.

We could relay the message calls from scene delegate to app delegate, and ask developers to only use AppDelegate. However, we lose the scene info during the relay for multi-scene apps. For example, if we simply relay sceneDidEnterBackground to applicationDidEnterBackground, we lose the info about which scene enters the background.

Proposal

Add SceneDelegate to the new project template.