Clutter Stage: Draw regions instead of bounding rectangle
This tracks finishing a performance optimization of https://bugzilla.gnome.org/show_bug.cgi?id=782344, the attachments https://bug782344.bugzilla-attachments.gnome.org/attachment.cgi?id=351368 and https://bug782344.bugzilla-attachments.gnome.org/attachment.cgi?id=351369
Drawing regions instead of the bounding rectangle leads to high overdraw in many scenarios, especially as more apps make better use of the Wayland API and, instead of repainting their whole buffer, tell us what to redraw.
This is especially bad in combination with #694 (closed)
Fixing this should hold substantial power-usage-reduction-potential in certain scenarios.
Edited by Robert Mader