Only the volume drawing part is really finished and exposed to the user. Hair
plugs into the existing hair rendering code and is fairly straightforward. The
pointcloud drawing is a hack using overlays rather than Eevee and workbench.
The most tricky part for volume rendering is the case where each volume grid
has a different transform, which requires an additional matrix in the shader
and non-trivial logic in Eevee volume drawing. In the common case were all the
transforms match we don't use the additional per-grid matrix in the shader.
Ref T73201, T68981
Differential Revision: https://developer.blender.org/D6955
This patch is (almost) a complete rewrite of workbench engine.
The features remain unchanged but the code quality is greatly improved.
Hair shading is brighter but also more correct.
This also introduce the concept of `DRWShaderLibrary` to make a simple
include system inside the GLSL files.
Differential Revision: https://developer.blender.org/D7060
