[glTF] Support bufferView stride (interleaved attributes)

[footballhead]

The current implementation of GltfLoader::LoadMeshData assumes that each attribute is stored tightly packed. However, glTF allows for interleaved attributes, see 3.6.2. Trying to load interleaved data like it is tightly packed results in garbage output.

BigWheels should support interleaved attributes in order to correctly load models like:

• BoxInterleaved

[footballhead]

A curious case of this is SimpleTexture; the UVs are stored as four triples: (U_1, V_1, 0), (U_2, V_2, 0), (U_3, V_3, 0), (U_4, V_4, 0). If you stride the buffer then you only read the UVs and skip the 0. However, if you don't stride then you read (U_1, V_1), (0, U_2), (V_2, 0), (U_3, V_3)