iOS 13+ always uses the scenes if there is one registered in the manifest

[mattleibow]

Description of Change

This PR fixes the issue of a secret double init of the main window on iOS 13+ on iPhone. Even though the iPhone does not support multi-window, it still uses the scene delegates and will just throw internally.

Additions made

• Move and correct the logic in the UIApplicationDelegate to not consider the platform type when scene delegates are used
• Make sure to return false for RespondsToSelector for GetConfiguration if scenes are not being used

[Redth]

Should we generate a partial info plist with the scene entries for MacCatalyst? I guess that won't work for iPad since that's still iOS tfm. Maybe we could do so off a project property?

At the very least this PR should remove the entry from iOS info plist in the template?

[mattleibow]

There is nothing wrong with using scenes on iOS. In fact, it is "recommended"?

In iOS 13 and later, use UISceneDelegate objects to respond to life-cycle events in a scene-based app.

However, it is also an opt-in feature:

Scene support is an opt-in feature. To enable basic support, add the UIApplicationSceneManifest key to your app’s Info.plist file

https://developer.apple.com/documentation/uikit/app_and_environment/managing_your_app_s_life_cycle

I have updated the PR to do this logic even more correctly and now we can support either scenario.