* Fix crash in GLTF2 Importer when a scene with dangling/uninitialized pointers gets deleted after an exception was thrown
* Fix crash in GLTF2 Importer when channel sampler is not set (negative index)
CUBICSPLINE interpolation has tangent values with the animation data.
Current import don't care this interpolation type but it will help not
to fetch tangent values instead of animation data.
Note: Assimp cannot support interpolation types yet.
Primary changes are to include/assimp/metadata.h, adding in the aiMetadata GetAiType function,
adding the operator= to allow an aiMetadata type to be assigned, adding a check for the
AI_AIMETADATA type flag as it can't be trivially memcpy'd.
operator= is implemented with a by-value argument as then the copy is made by the copy
constructor and we can just swap everything out and let the destructor handle the mess.
Implemented parsing of the "extensions" flag on all glTF2 Nodes. Doesn't use the ReadValue
helper function on numbers as it did not seem to fill out the Nullable structure properly.