- EngineEnums.h is not a private headers as it contained mostly private
stuff
- MaterialEnums.h is still public, but now only contains public stuff.
Private parts were moved to MaterialEnums.h or MaterialBuilder.h
- And finally SamplerBinderMap is moved under private/ as well, since
it's certainly not a public API.
With this change, the public headers of filabridge become more reasonable
and limited.