to reflect how we usually expect these events to look

- Stop an active single-touch drag if the user adds additional fingers
  and touchZoomRotate is enabled, so the latter can take over interaction
- Start a single-touch drag if the user removes all but one finger
- Add tests for expected single vs. multi-touch interactions

Additional tests/cases to capture the fact that we
only expect touchZoomRotateHandler to take over once
we've actually begun zoom/rotate gesture; two-finger
straight pan should still be handled by dragPanHandler.

See comment on #8100 for more details.

Tests currently failing.

Co-authored-by: Anjana Vakil <anjana.vakil@mapbox.com>

Co-authored-by: Arindam Bose <arindam.bose@mapbox.com>

Co-authored-by: Arindam Bose <arindam.bose@mapbox.com>

To account for the fact that move event handlers might be
inspecting the DragPanHandler's (in)active state, update
the state in the onMove handler rather than in onDragFrame.
However, don't fire the dragstart/movestart events
immediately on the move event as we had been doing before;
schedule these to be fired on the first drag frame.

Co-authored-by: Arindam Bose <arindam.bose@mapbox.com>

Co-authored-by: Arindam Bose <arindam.bose@mapbox.com>

…n .deactivate()