Blender Git Loki

DRW/Eevee: Add correct support for Orco

Until now, Orcos were computed by the gpu (GLSL) and were not taking into
account the modifier stack (breaking orco for deformed mesh).

Now Orco is now computed on CPU but only if a modifier stack is present.

Tagging that an ORCO layer is present is done via a 4th component, which is
a waste of memory/bandwidth. Best would be to do the same as auto attrib
color space and save a bool uniform somewhere but for now it's too
disruptive.