Shader Translation Graph from `standard_surface` to `open_pbr_surface`

[jstone-lucasfilm]

This is a proposal to create an initial Shader Translation Graph from standard_surface to open_pbr_surface, allowing assets created in the first shading model to be well approximated in the second shading model, with any required visual compromises being publicly documented.

There's a small set of existing shader translation graphs in the MaterialX repository, which could make a good reference and starting point for this task:

https://github.com/AcademySoftwareFoundation/MaterialX/tree/main/libraries/bxdf/translation

Additional resources:

• https://materialx.org/assets/ASWF_OSD2021_MaterialX_slides_final.pdf#page=16
• https://github.com/AcademySoftwareFoundation/MaterialX/blob/main/libraries/bxdf/standard_surface.mtlx
• https://github.com/AcademySoftwareFoundation/MaterialX/blob/main/libraries/bxdf/open_pbr_surface.mtlx

[jstone-lucasfilm]

Following up on this task, @mkuo-lucasfilm has expressed interest in taking a look during her Summer 2024 internship at Lucasfilm. Thanks @mkuo-lucasfilm!