UIKitBackend: Update to use UIScene lifecycle

[stackotter]

When debugging a SwiftCrossUI UIKitBackend app via Xcode, you get the following warning;

CLIENT OF UIKIT REQUIRES UPDATE: This process does not adopt UIScene lifecycle. This will become an assert in a future version.

[bbrk24]

This is, technically, a user error. You just have to update your Info.plist to tell it the scene delegate is UIKitBackend.SceneDelegate or a subclass thereof

[stackotter]

Ah ok, sounds like something Swift Bundler will have to handle then. We'll somehow have to have a way for Swift Bundler to detect what scene delegate to use (in order to have a smooth user experience).