Ensure that OverscrollEffect.applyToFling() is called

This CL ensures that we always call OverscrollEffect.applyToFling() when
stopping a drag, and that this is called on the nested dispatcher scope
so that the call won't be cancelled even if the draggable node is
removed.

Bug: 378470603
Test: atest NestedDraggableTest
Flag: EXEMPT new API not used anywhere yet
Change-Id: I306cac168b7b97e70a6d762c133cb22d5bdf14b4