Expose OBJFileLoader options to scene loader APIs

[ryantrem]

This is a small change that exposes the existing ObjFileLoader options through the new scene loader functions. The focus at the time was glTF and this just wasn't on the radar, but there is a real use case for it now.

• Allow a subset of options to be passed to OBJFileLoader. Any that are missing will get the default. This is fully backward compatible with the existing API.
• Plumb OBJFileLoader options through the dynamic loader factory (same as other loader plugins).

[bjsplat]

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[bjsplat]

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[bjsplat]

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