Rotating an output would show duplicate cursors when the pointer is
located over an area which would be within the output if not rotated.
Make sure to swap the width/height of the output when rotated.
Closes: https://gitlab.gnome.org/GNOME/mutter/issues/85
(cherry picked from commit ebff7fd7f4ee2c9636412fe661a1fbdf51f218a0)