This patch implements the multi-function procedure operation for the new
CPU compositor, which is a concrete implementation of the PixelOperation
abstraction, much like ShaderOperation, but uses the FN system to more
efficiently evaluate a group of pixel-wise operations.
A few changes were done to FN to support development. The multi-function
builder now allows retrieving the built function. A new builder method
construct_and_set_matching_fn_cb was added to allow using the SI_SO
builders with non static functions. A few other SI_SO were added to. And
a CPP type for float4 was added.
Additionally, the Gamma, Math, Brightness, and Normal nodes were
implemented as an example. The Math node implementation reused the
existing GN math node implementation, so the code was moved to a common
file.
Reference #125968.
Pull Request: https://projects.blender.org/blender/blender/pulls/126988
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