DragController methods return the consumed gesture

To make it easier to handle nested scroll gestures, the onDrag and
onStop methods now provide information about how much of the gesture was
 consumed by the STL.

Test: atest DraggableHandlerTest
Bug: 336710600
Flag: com.android.systemui.scene_container
Change-Id: I2596d284cfba3f89135bf1485eb35655fe6ee47d