This modify the GBuffer layout to store less bits per closures.
This allows packing all closures into 64 bits or 96 bits.
In turn, this reduces the amount of data stored for most
usual materials.
Moreover, this contain some groundwork for the getting rid of the
hard-coded closure type. But evaluation shaders still use
the hard-coded types.
This adds tests for checking packing and unpacking of the gbuffer
doesn't loose any data.
Related to #115966
Pull Request: https://projects.blender.org/blender/blender/pulls/116476
f4275cc4df