WIP: Support loading meshes with heterogeneous polys

[Jean-Francois-Lafleche]

Load meshes with heterogeneous polys by converting all faces to triangles.

• Created a new asset for testing (rocket.obj) which includes heterogeneous polys
• Updated Mesh class to automatically convert heterogeneous polys to triangles when detected
• Updated USD tutorial now that heterogeneous polys can be loaded
• Updated USDMeshes class to allow loading of heterogeneous polys meshes
• Updated relevant tests
• Added test for loading obj with mixed heterogeneous polys

[Jean-Francois-Lafleche]

Per comments from Clement, the following needs to be done:

• Move the USD creation out of visualizer module, since it no longer does visualization without Kit integration
• Clarify the tutorial regarding visualization and write the steps needed to visualize using currently available visualizers (trimesh).

[Caenorst]

Can you force push to trigger the CI ?