This makes it possible to have fully allocation-less MeshData, with
statically defined indices and attributes. Only the final MeshData
construction needs to be done at runtime because Array is not constexpr,
but that isn't anything heavy anyway.
With API analogous to the (relatively) new AnimationData -- with one
buffer containing all index data and one buffer containing all vertex
data, both meant to be uploaded as-is to the GPU.
This will eventually replace MeshData2D and MeshData3D, backwards
compatibility and wiring up to other APIs will be done in follow-up
commits.
Vladimír Vondruš