Blender Git Loki

EEVEE: SSRayTrace: Cleanup/Refactor

This is a major rewrite that improves the screen space raytracing
a little bit.

This also decouple ray preparation from raytracing to be reuse in other
part of the code.

This changes a few things:
- Reflections have lower grazing angle failure
- Reflections have less self intersection issues
- Contact shadows are now fully opaque (faster)

Unrelated but some self intersection / incorrect bad rays are caused by
the ray reconstruction technique used by the SSR. This is not fixed by
this commit but I added a TODO.