Support ArnoldGinstance prims in hydra

[sebastienblor]

Arnold shapes are supposed to be supported in Hydra, as native_rprim.cpp and shape_adapter.cpp.
They're also listed as rprims in the schemas.

When an ArnoldProcedural prim is found in a usd file through hydra, it goes through the expected code and renders it with Arnold, same with ArnoldVolume, etc... However, ArnoldGinstance doesn't seem to be supported. It doesn't even go through HdArnoldRenderDelegate::CreateRprim despite it being part of the list returned in GetSupportedRprimTypes()

This can be seen in test_0079 (which is test that converts a test.ass into usd and then kicks it).
As a comparison, test_0067 has a primitive ArnoldProcedural that renders fine

[autodesk-oss-arnold-bot]

Issue synced internally to ARNOLD-15352