Make sure that IRemoteAnimationController is always triggered.

When an app transition is executed, RemoteAnimationTarget instance is
created for apps and IRemoteAnimationController#onAnimationStart is
called.
However it's possible that no valid app exists when an app transition is
executed, for example, an activity doesn't resume before timeout. If it
happens, RemoteAnimationController triggers
IRemoteAnimationController#onAnimationCancelled.

Test: atest RemoteAnimationControllerTest
Bug: 175687166
Change-Id: I50ddc91f7bd7ed24a977fa3face9c6e56e1bea02