Only send mouse move event when mouse moves

Qt Quick recently changed to send hover events 60 times per second even
if the mouse doesn't move. Make sure we only send mouse move events
over the Wayland protocol if the mouse actually moved.

Change-Id: Ic196512dde1718de461eb2c64cec2e95e220ce89
Reviewed-by: Johan Helsing <johan.helsing@qt.io>