Merge Vertex Indices in USD.

**Describe the bug**
In Obj context you can merging of the indices and data of coincident and identical vertex attribute values (**Merge Vertex Indices**) but there is no way to do it in USD. This makes textures stretching when you add subdivision on surface. If disable merging vertex indices in Obj you get the same result as in Solaris.

**To Reproduce**
There is Houdini scene to reproduce issue:
[check.v001.hip.zip](https://github.com/Autodesk/arnold-usd/files/11337409/check.v001.hip.zip)

**Screenshots**


**Used Software Versions**
- Arnold: [e.g. 7.2.1.1]
- Houdini

Start with the attached check.v001.hip.zip Houdini scene and compare the USD result with Obj behavior when Merge Vertex Indices is enabled or disabled. Reproduce the subdivision texture stretching and inspect the USD path involved; done means coincident and identical vertex attributes are merged in USD so the result matches the intended Obj behavior without stretching.

Written by the indexing model from the issue text.