Implement wl_surface::damage_buffer

Summary:
Missing from our surface handling was the damage_buffer call introduced in
version 4 of the wl_compositor interface.

Its only difference to a normal damage call is that the damaged region is
supposed to be defined by the client in buffer coordinates instead of
surface coordinates. This damage must be tracked separately in KWayland
and on commit with the buffer transformation united with the normal damage.

Test Plan: Autotest updated.

Reviewers: #kwin, davidedmundson

Reviewed By: #kwin, davidedmundson

Subscribers: davidedmundson, zzag, kde-frameworks-devel

Tags: #frameworks

Differential Revision: https://phabricator.kde.org/D15910