USD assets are missing collision geometry

[mmacklin]

USD assets like G1, H1, and ANYmal have incomplete collision geometry which means they penetrate the ground when simulating:

#639 (comment)

Ideally assets should be configured with approximate collision so they collide with the ground / static environment correctly out of the box, and have a way (can be programmatic or variant based) to disable certain collision shapes for performance, or enable self-collision for higher fidelity.

[preist-nvidia]

We want to use the same or similar assets as in lab for the examples and benchmarking.

But we can enable additional collisions with a switch when the example is run with the viewer.

Another approach is to display collision geometry by default to make it clear that we are running collision-geometry-optimized models. We need a switch in the viewer for visual vs. collision geometry.