* Using standard NDF and Smith shadowing-masking terms. The previous
`xxxx_opti()` functions were faster to evaluate, but confusing and
error-prone.
* After correcting the BRDF pdf, the prefiltered environment LOD bias
needs to be adjusted to avoid overblurred reflections.
* Corrected the half-vector computation in BTDF evaluation, added check
for invalid configuration due to total internal reflection or `eta == 1`.
* Use `saturate()` instead of `max()` when no division is needed because
the former is faster.
* Indirectly fixes EEVEE-Next refraction denoising.
Pull Request: https://projects.blender.org/blender/blender/pulls/111591
8a735d0aa4