framebuffer: Don't mark the clip dirty at mid scene

https://bugzilla.gnome.org/show_bug.cgi?id=712562
framebuffer: Fix clip tracking in the unclipped case

Leaving the clip bounds untouched means that it will retain the stale value
of whatever it was when we last had a clip; reset it so that it contains the
full framebuffer contents instead.

https://bugzilla.gnome.org/show_bug.cgi?id=712562
cogl-texture-2d: Add update_area equivalent for Wayland