compositor: Fix partial repaints

compositor: Fix partial repaints

Partial repaints have been broken since the introduction of the atomic
surface updates. The problem was that surface_commit would set the
geometry dirty flag unconditionally, causing transform updates on every
frame which would in turn cause weston_surface_damage_below() to damage
the whole surface area.

This patch changes this so that flag is only set if the pending buffer
has a different size, the location of the surface changed or the opaque
region changed.

Note that changing the opaque region will cause a full repaint of the
affected surface, because of the transform update.

https://bugs.freedesktop.org/show_bug.cgi?id=56538