NOT-FOR-UPSTREAM: gl: Cache glyph masks

This avoids the overhead of constantly binding new framebuffers, which
can be very slow on non-Intel hardware. See:
http://lists.cairographics.org/archives/cairo/2013-February/024073.html
CHERRY-PICK: gl: Set up operands when the vertex size changes

Previously _cairo_gl_composite_setup_vbo was overwriting the old context
vertex_size, while _cairo_gl_context_setup_operand was relying on it to
determine if the vertex size changed. Instead of a fragile ordering of
statements, pass whether the context changed as an argument to enforce
the calling order via method parameters.
CHERRY-PICK: gl: Fix typo in gles2 shader cache lookup

When comparing shader cache entries, it's important that we actually
compare the variable type hash.
CHERRY-PICK: gl/msaa: Resolve multisampling on surface flush

When flushing a surface, we must resolve multisampling for desktop GL.
This allows use of the original surface texture in any following raw GL
operations. This fixes accelerated canvas with WebKitGTK+ using the MSAA
compositor.
CHERRY-PICK: gl: Separate framebuffer bind from destination selection

Disentangle the action of binding the framebuffer from setting the
destination. This straightens up the code a bit and avoids some redundant
operations (such as reacquiring the context) when simply switching from
the multi-sample framebuffer to the single-sample framebuffer and vice
versa.
CHERRY-PICK: gl: Update transformation when surface size changes

In my previous commit I mistakenly removed the transformation matrix
update when cairo_gl_surface_set_size is called. This change restores
it.