xcb: send QTabletEvent before QMouseEvent

xcb: send QTabletEvent before QMouseEvent

It was a regression: drawing applications which can handle both mouse
and tablet events should not need to wait to see whether a mouse event
will be followed by a corresponding tablet event.  The tablet event is
preferred because it has all the tablet parameters (pressure etc.)
Also, show the timestamp of each mouse event in the log message,
which helps to verify the correspondence.

Task-number: QTBUG-47702
Change-Id: I9e832c19de935ec1243138eb4c1484284f61cbfc
Reviewed-by: Laszlo Agocs <laszlo.agocs@theqtcompany.com>