Support mesh splitting for meshes with more than 8 materials

[Geenz]

Adds support for splitting glTF meshes when they have more than 8 materials. This works around a platform limitation where objects may have up to 8 faces.

This adds parity for the COLLADA importer's ability to split meshes with more than 8 materials.

Test Plan

1. Pick a glTF mesh that has more than 8 materials on a specific sub-mesh
2. Upload the mesh - ensure that the mesh was split into multiple meshes

[aiaustin]

Models uploaded with first Project Viewer 7.1.14.15361077240 - Second Life Project were given base colour and only materials with a texture for base colour were white. This was very useful to act as a guide for applying materials, especially for models with a lot of materials.

Models (unrigged) uploaded with latest version Second Life Project Gltf Mesh Import 7.1.14.15453847512 are all white.

Image shows yesterday's uploaded item as it appears when uploaded before proper materials application, and the white model in front is today's upload of the same model.

Could the changes being made for this issue have caused this regression?

[akleshchev]

Could the changes being made for this issue have caused this regression?

Yes, I had to change how they distribute, but missed that they were initialized. Fix is trivial, preparing it for review.

[aiaustin]

For the core issue being addressed here, the NASA Perseverance Rover Model could be a useful test mesh as the model has some objects with > 8 materials on parts.

https://nasa3d.arc.nasa.gov/detail/perseverance

There is a .blend and .glb file there. The GLB has one validation error as one material seems to have a metallic property > 1 (1.00001 or something like that!). If critical to testing, that can be removed by using the .blend file version and changing the material before reexport. I just altered the IOR of all materials to 1.5 (some were 1.445) and reexported and the GLB was then valid. The embedded animation also can be removed on export if that is not ignored by the Second Life Mesh Uploader (though I assume it is).