Add triangle/ray and gltf/ray intersect function with tests

[joseph-kaile]

Added two new utility functions, rayTriangle and intersectRayGltfModel. They have unit tests to verify their correctness.

This PR can really be thought of as two distinct efforts:

• The implementation of ray triangle intersections in a mathematically correct and performant way
• glTF traversals that are robust and support all reasonable use cases. A good bit of coding was devoted this. Also notable, the glTF test data was generated using python scripts.

[csciguy8]

Still, the code in this PR just relied on existing functionality. Nobody can expect someone who uses the OrientedBoundingBox to look into the constructor code and see whether there might be an open TODO (of which nobody knows how to resolve it).

I'm thinking we should make this a separate issue, and not handle it for this PR.

I do have opinions of course (like letting the OBB constructor code throw), but this feels like something to be discussed outside of ray intersection tests.

[csciguy8]

@kring Ready for one more pass!

[kring]

Looks good, thanks! I'll merge as soon as CI passes.