Refactor detectDragGestures in MultiPointerDraggable

The horizontalDrag and verticalDrag methods have been replaced with
their current implementation.
However, these methods do not currently handle ignored events (those
that are not hasDragged).

Support for these events will be added in a later CL.

Test: No new test, simple refactor
Bug: 345434452
Flag: com.android.systemui.scene_container
Change-Id: I6a0ac353bf563132fcfa33bf7100e3d9f216c53e