Support place2dTexture nodes

This might be difficult since glTF doesn't have a notion of this, meaning we should bake the UV transformations in the UV coordinates...

There does seem to be an extension to support transforming textures: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_texture_transform

Please also note that there's been some discussion on the rotations it applies and whether it's inverted or not. So if you get wrong results it might be related: https://github.com/KhronosGroup/glTF/issues/1563