Improve SceneGestureHandlerTest tests to support suspended methods calls

We need to refactor the SceneGestureHandler class (see ag/25757212) to
prevent multiple jobs from running concurrently and to enabling the
onDrag() and onDragStopped() methods to return the amount of
offset/velocity consumed.

This CL updates the tests to support both implementations.

Test: atest SceneGestureHandlerTest
Bug: 317063114
Flag: NA
Change-Id: I1662e59f94925199b4f157fc34e4b7060f11874b