Short term:
[x] Initial implementation {D13533}
[ ] Solve potential issues with motion blur
[ ] Walk without relying on UV maps for consistent directions
[ ] Metal GPU support
[ ] Separate MNEE code from `shade_surface` kernel somehow, running before or after?
[ ] Separate shader ray-tracing and MNEE versions of `shade_surface` kernel?
Longer term:
[ ] Extend to more general specular manifold sampling, for reflective caustics
[ ] Integrate with path guiding