This simplifies the GBuffer packing code in a lot
of common use cases. This improves compilation
speed.
The trivial case is either a single closure (already handled)
or 2 closures with no second data layer.
We detect if reflection and refractions can
be assumed colorless depending on the nodetree config.
Colorless reflection or refraction are only using one
data layer.
Pull Request: https://projects.blender.org/blender/blender/pulls/146455
fdd8d85f89