New implementation of hair for Eevee.
Note: A hard coded "transmission" property is being used. This should
eventually be exposed to the UI, possibly in the form of SSS
properties.
This still has a couple of issues:
* Instancing is not working when multiple particle systems use the same
primitive. Only the last particle system to be drawn with a particular
primitive shows up.
* Because of colors being passed as uniforms with static variables, the
color of the collection of the last object to be evauluated is used for
all particles being displayed.
Also, note that while this is being drawn in the clay engine, this might
be moved to the object mode later intead.
Part of T51378
