This modify most shader using the GBuffer to use the
`ClosureUndetermined`. This in turn reduces the amount
of duplicated data in the `GBufferReader` structure.
The most important part is the usage of fixed array
indices to access the `GBufferReader.closures[]`.
This avoid the struct to be moved from local register
to device memory and remove a huge performance penalty.
Pull Request: https://projects.blender.org/blender/blender/pulls/116772
f2b3403145