This class will not extend well to glTF so this cordons it off into the
filamesh namespace, which is an already-existing namespace that we use
for the things related to the filamesh file format.
For glTF we might create a new library with its own MeshReader so
this will mitigate confusion.
* Add clear coat normal map support
This change allows to set a separate normal map for the clear coat layer of a material.
* Document the new clearCoatNormal property
* Fix typo
