VideoCommon: add functionality to prepare for a custom mesh asset to be used by graphics mods

[iwubcode]

This adds the loading logic for a mesh asset. The actual library implementation to load the mesh will be added in a subsequent PR to keep things smaller.

The idea is that meshes will be imported from a GLTF file (using a new external tinygltf) and will be stored in a Dolphin binary file that mimics the mesh data needed by Dolphin (as well as a json file, which contains metadata that is modifiable by the editor, currently a mapping between GLTF material name and Dolphin material asset).

Each part of the model file is loaded into a "chunk" which contains all the data needed to render that sub-mesh (the transform used for orientation, the material name on the original GLTF file, and the actual vertex data used to render) and the renderer just loops over all the chunks to draw the model

This logic is pulled from #12280 where there is an import menu, along with logic to render that mesh (coming later).

[iwubcode]

Things left for future work:

• Create Dolphin materials from GLTF materials
• Pipeline changes to support various samples (iridescence, culling, etc): https://github.com/KhronosGroup/glTF-Sample-Assets/blob/main/Models/Models-testing.md
• Some models still fail to load (ex: anything that requires doubles or u32 indices)