When there was no root background pixmap, we were using a 1x1 repeating
texture as a simple way of drawing a solid color without adding a
second code path. However, when that 1x1 texture was combined into
a larger "atlas texture", hardware repeat couldn't be used, so a
small inefficiency from this approach became an enormous inefficiency
as clutter drew every pixel of the background as a separate rectangle.
https://bugzilla.gnome.org/show_bug.cgi?id=652507
Create new cogl-utils.[ch] and move a helper function from
MetaShadowFactory there as meta_create_texture_material(); this
allows us to create single-layer materials from different parts of
Mutter and have them share the same template material.
Also expose a function for creating a 1x1 texture of a given
color meta_create_color_texture_4ub().
https://bugzilla.gnome.org/show_bug.cgi?id=634833
