Introduce RemoteAnimationDelegate.

This interface represents a runner for a remote animation capable of
handling custom implementations of IRemoteAnimationFinishedCallback.

In practice, it will enable us to swap in
ActivityLaunchAnimator.AnimationDelegate as a delegate inside
LauncherAnimationRunner, thus enabling the use of the animation
library for activity launches in Launcher.

Bug: 250588519
Test: tests still passing, plus manual on the Launcher side
Change-Id: I9dbfca07bbd5d18900711008bb39bb131f3ecc76