Blendshapes without a skeleton already worked.
However, due to a faulty ERR_FAIL_COND, it was impossible to create a mesh with both bones and blendshapes.
This also fixes an assumption that all surfaces reference the same number of bones as surface 0.
* Support KHR_texture_transform.
* Support exporting glTF2
* Support exporting instanced scenes
* Extract into a gltf state and gltf document
* Add a tools menu for exporting gltf2