UsdGeomTetMesh: unexpected imaging behavior with primvars

[cameronwhite]

Description of Issue

Hydra displays UsdGeomTetMesh by showing its surface triangles, but this appears to also pass along any primvars from the tet mesh to the triangle mesh without further validation, which can cause problems with uniform or faceVarying interpolation. For example, if there is a uniform primvar with a value for each tetrahedron, this may not match the ordering or number of surface triangles. The attached files demonstrate this with primvars:displayColor, showing the TetMesh side by side with the expected result as a Mesh

Steps to Reproduce

1. From the attached file (tetmesh_primvars.zip ), open either of the .usda files in usdview. One file has the same number of tets as surface triangles and shows the colors being displayed in an unexpected order, and then other contains a single tet where the colors aren't displayed by Storm due to the primvar having fewer values than the number of surface triangles.

System Information (OS, Hardware)

Ubuntu 22.04

Package Versions

USD 24.03