Add BCSDF Approximation for Second Hair Material Type (#4935)

* Initial commit of the marschner infrastructure (LUT/LTC, Analytic BSDF, ShaderGraph, etc.)

* Initial commit to add scattering mode dropdown

* Add the framework for a preintegrated Marschner FGD

* Re-hide the material type for hair

* Correct some slight typos

* Un-hide the hair material type

* Initial commit strand count estimation from density volume

* Initial work for Surface to BSDF data

* Initial readdition of the hair reference

* Adapt the reference to use the new BSDF data

* Use the reference for the raster BSDF

* Add the first lobe approximation

* Initial commit TRT approximation

* Add TT attenuation term

* Further simplify the attenuation TT

* Add roughened azimuthal scattering, remove IOR param, add TT distribution

* Initial work for environment evaluation

* Add the approximated scattering mode. Move the environment evaluation to post evaluate BSDF

* Disable area lights for Marschner (temporary until LTC is fixed for anisotropy)

* Use the newly fitted gaussian coefficient LUT for azimuthal transmission roughness

* Readjust the gaussian fit for azimuthal roughness

* Skip TT lobe for environment sample

* Improve Parameterization: Longitudinal Roughness -> Smoothness

* Improve Parameterization: Azimuthal Roughness -> Radial Smoothness

* Optimize the math for spherical coordinate angles.

* NaN suppression

* Revert back from sine theta to the half angle for longitudinal scatter

* Fix all the warnings

* Re-enable area light and fall back to GGX like Kajiya

* Add note regarding Marschner pre-integration

* Update hair graphics test

* Update some reference images for Vulkan/Metal due to some shadow cascade discrepancy

* Remove the primary reflection smooth parameter.

* Roughness clamping for longitudinal scattering

* Rename Use Light Facing Normal to Geometry Mode (Cards, Strands)

* Documentation - First Pass

* Rename Geometry Mode -> Geometry Type

* Tooltips - Also hide the Scattering Mode until the improved approximation is merged.

* Incorporate documentation feedback

* Fix an issue with documentation bulletin

* Fix an issue with a shader graph asset breaking the hair test

Author: johnpars

TestProjects/HDRP_Tests/Assets/GraphicTests/Scenes/1x_Materials/1401_HairGraph.unity

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