Blender Git Loki

DRW: Fix/refactor UBO & Texture binding.

Previous approach was not clear enough and caused problems.
UBOs were taking slots and not release them after a shading group even
if this UBO was only for this Shading Group (notably the nodetree ubo,
since we now share the same GPUShader for identical trees).

So I choose to have a better defined approach:
- Standard texture and ubo calls are assured to be valid for the shgrp
they are called from.
- (new) Persistent texture and ubo calls are assured to be valid accross
shgrps unless the shader changes.

The standards calls are still valids for the next shgrp but are not assured
to be so if this new shgrp binds a new texture.

This enables some optimisations by not adding redundant texture and ubo
binds.