Introduce FlingOnBackAnimationCallback to make use of new timestamp API

With the new frameTime field in BackEvent, velocity can be calculated on the client side. Therefore this CL introduces a FlingOnBackAnimationCallback that automatically animates back gesture flings.

Bug: 362938401
Test: FlingOnBackAnimationCallbackTest
Flag: com.android.window.flags.predictive_back_timestamp_api
Change-Id: I3bcf0ef23ab0171cbd8326ad4e0d548dcf87b334