Revert "Remove DepartingAnimationTarget from BackMotionEvent(2/2)"

Revert submission 32129017-remove_departing_motion

Reason for revert: b/402422333

Reverted changes: /q/submissionid:32129017-remove_departing_motion

Change-Id: Id3dab47ddac90de8564379ce41cb7943bfb31fa4
1 file changed