Cancel transition when pointer input is cancelled

This CL fixes a bug in MultiPointerDraggable: before this CL, we would
not call onDragStopped() when the current pointer input was cancelled
(for instance because enabled became false). With this CL, we ensure
that onDragStopped is always called if onDragStarted() is called.

Bug: 308961608
Test: MultiPointerDraggableTest
Flag: N/A
Change-Id: I20561ba10533380cd16b69f4146851fbb9abb008