material: Support sparse ARBfp program generation

material: Support sparse ARBfp program generation

We don't need to generate a new ARBfp program for every material created
if we can find an ancestor whos state will result in the same program
being generated.

The more code we can have adopt the coding pattern of deriving their
materials from other similar materials using cogl_material_copy() the
more likely this metric will be good enough on its own to minimize the
set of arbfp programs necessary to support a given application.