We cannot fully deprecate Geometry, because ClutterActor and ClutterText
are actually using the type in signals and properties; but we can
deprecate the API that uses this type, so that 2.0 will be able to avoid
it entirely.
Since the code dealing with ClutterShader is pretty self-contained, now,
we can safely move it outside of the main ClutterActor source file and
into its own. This will allow us to just drop a bunch of files when
branching for 2.0.