Include Intel Open Image Denoiser as a 2d node

[statixVFX]

Summary

Include a node that uses the Intel Open Image Denoiser library so we can denoise with cycles as a post-process.

User story

What

OIDN is super fast and super useful for the majority of path-tracers. Including cycles. Runs CPU/GPU and would be a valuable tool in gaffer for cycles users.

We already use it inside of blender when rendering with cycles, but moving to gaffer we've yet to come up with a better workflow without it

Why

Various denoising methods are needed, and OIDN is one of the best ones for spatial denoising CG renders.

Feature proposal

As a 2d node, with standard inputs for albedo, normals and depth.

https://www.openimagedenoise.org/

[boberfly]

https://github.com/boberfly/GafferDenoise just needs dusting off and refinement.