Utility to delegate to a different RemoteTransition for each transition.

We're creating a new remote transition in Launcher for cross-display app
launches. That remote transition should override certain existing code
paths for app launch transition handling.
To be able to override existing (legacy) remote handling we here provide
a remote transition utility that allows the caller to decide which
RemoteTransition to use for each transition.

Bug: 422333177
Flag: com.android.window.flags.enable_cross_displays_app_launch_transition
Test: RemoteTransitionDelegatePickerTest
Change-Id: I9d032488521de01cbc3dff9dc960b8551129842b