Improvements for stopping animations in SceneGestureHandler

The following improvements have been made:
- on onDragStarted(): When a new transition begins, the current
animation is stopped and the current drag offset is immediately obtained.
- New log: If the transition is a generic TransitionState.Transition, a
log is added, since it is not fully supported at the moment.
- on onDragStopped(): An animation has been added when the animation is
stopped when the state is TransitionState.Transition.
- on animateOffset(): animateOffset no longer waits for the coroutine to
 complete to reset the isAnimatingOffset state.

Test: atest SceneGestureHandlerTest
Bug: 291025415
Change-Id: I3d04ea2a2c822a2b17b377046d43a31757dcbd19