clutter-stage-x11: Don't ensure the viewport when the window moves

clutter-stage-x11: Don't ensure the viewport when the window moves

When we receive a ConfigureNotify event that doesn't affect the size
of the window (only the position) then we were still calling
clutter_stage_ensure_viewport which ends up queueing a full stage
redraw. This patch makes it so that it only ensures the viewport when
the size changes as it already did for avoiding queueing a relayout.

It now also avoids setting the clipped redraws cool off period when
the window only moves under the assumption that it's only necessary
for size changes.