Add support for multiple texture images

[csparker247]

New versions of our photogrammetry reconstruction pipeline can produce meshes with multiple texture images (pgs-recon!23). However our code doesn't support this really at all. Here's a short list of things that need to be updated:

• New/updated mesh structure which supports multiple textures
• Updated OBJReader which can read multiple textures/materials
• Update ReorderUnorganizedTexture to handle multiple textures

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Migrated from GitLab issue 69 originally opened by @csparker247 on 2024-06-12.