animateOffset can partially consume the fling velocity

When a scene is configured to disallow overscrolling
(`overscrollDisabled()` is enabled), a fling gesture on that scene may
not use up all of the velocity. The unused velocity can then be passed
on to the ancestor of the component.

Test: atest DraggableHandlerTest
Bug: 336710600
Flag: com.android.systemui.scene_container
Change-Id: Ia1b0620fe37cfaf5b339d1e87c38ba5c22be95e8