Samplers are now imported into assimp internal format from textures;
Samplers have defaults as per spec;
Sampler enums are strongly typed with UNSET values;
Samplers are exported properly;
Sampler filters are exported as well;
Samplers are re-used across textures on export
Default sampler values are not written
pbrMetallicRoughness and pbrSpecularGlossiness as structs; persist textureinfo properties from start to finish; persist pbrSpecularGlossiness (via extensionsUsed) usage from start to finish
Daniel Hritzkiv