animateOffset returns the consumed velocity after the animation ends

This change enables us to wait for the animation to finish and allows us
to obtain the velocity computed at the end of the animation, even if
it's interrupted.

Test: atest DraggableHandlerTest
Test: atest PriorityNestedScrollConnectionTest
Bug: 336710600
Flag: com.android.systemui.scene_container
Change-Id: I91163d53f06b4622369db29ff7f9b2468ca6ac57