Incorrect drawing if prim is partially transparent / semi transparent

**Describe the bug**
A clear and concise description of what the bug is.

Hi,
We found a drawing issue in **VP2 render delegate mode** if the prim has some of the faces transparent, attached USD file (_partially_transparent_prim.usda_) is the super simplified version of one of our production assets.

The geometry's first face (index 0) has been rotated to x+ and has the opacity value set to 0; the inner faces are in red color and the outer faces are in blue color.

When viewing in usdview, the result is displaying as expected:

but in *mayaUsd-0.9.0*, the result is inccorect:

**Steps to reproduce**
Steps to reproduce the behavior:
1. Launch Maya and load the attached USD file;
2. Rotate and see the result

**Expected behavior**
Expect to match usdview / have the prim drawing correctly.

**Attachments**
[partially_transparent_prim.zip](https://github.com/Autodesk/maya-usd/files/6439464/partially_transparent_prim.zip)

**Specs (if applicable):**
- OS & version Centos 7.4
- Compiler & version gcc 6.3.1
- Maya version Maya 2020
- Maya USD official 0.9.0 release
- Pixar USD official USD-20.11 release

Start by loading the attached partially_transparent_prim.usda file in Maya with VP2 render delegate mode, then rotate the view and compare the result with usdview. Investigate the transparency behavior for the prim's face with opacity 0 and verify the inner red and outer blue faces. Done means Maya draws the partially transparent prim as expected, matching usdview.

Written by the indexing model from the issue text.