Reflection environment refactor, optimization and clean up. Fixed blending bug with layered cubemaps. Added diffuse from captures as alternative to lightmaps. Still tied to cvar.
[CL 2059445 by Brian Karis in Main branch]
* Static sky lights are now allowed, baked into lightmap
* Stationary sky lights are baked into low quality lightmap
* Baked sky lighting can only support emissive input to avoid a feedback loop
* Adaptive refinement quadtree nodes are now pooled as Lightmass builds were 7x slower with the FBinnedAllocator otherwise
* Specializations of SHBasisFunction which saves 10% of lightmass build times with sky lighting
* Dark texels have their directionality's contribution to the lightmap min and max dampened
[CL 2055868 by Daniel Wright in Main branch]
