Simplify the swipe offset animation logic

This CL simplifies the logic when animating the offset of a swipe
transition, after the user lifted their finger. The previous
implementation was made more complicated just to avoid allocating more
than one Animatable per SwipeTransition, which does not really have an
impact on performance anyways.

Bug: 290930950
Test: atest DraggableHandlerTest
Flag: N/A
Change-Id: I7b0d4bb1c6f29a3bfc02778e2fe8b03e80b5a6be