* Store compact ray differentials in ShaderData and compute full differentials on demand. This reduces register pressure on the GPU. * Remove BSDF differential code that was effectively doing nothing as the differential orientation was discarded when making it compact. This gives a 1-5% speedup with RTX A6000 + OptiX in our benchmarks, with the bigger speedups in simpler scenes. Renders appear to be identical except for the Both displacement option that does both displacement and bump. Differential Revision: https://developer.blender.org/D15677