Alembic primvars with "varying" in the name don't work in Solaris

**Describe the bug**
If you export a shape with varying user data to alembic, and the parameter is named something like "mtoa_varying_Pref" or "test_varying_Pref", then in Solaris that primvar does not work.

**To Reproduce**
Steps to reproduce the behavior:
1. Extract [arnold-abc-test.zip](https://github.com/Autodesk/arnold-usd/files/11003076/arnold-abc-test.zip). It has an abc exported from Maya with Arnold > Scene Export > Export Selected to Alembic. In Maya, the shape has varying user data named "test_varying_Pref" (it was named "mtoa_varying_Pref" but I changed it to "test").
2. In Solaris, use the Sublayer LOP to bring in the abc file
3. Assign a material that uses a user data shader to access "test_varying_Pref"
4. Render. You get the default color from the user data shader.

With "mtoa_varying_Pref" as the attribute name, here's the ultimate differences in usda.
Arnold Alembic export:
```
custom point3d[] primvars:Pref (
interpolation = "varying"
)
point3d[] primvars:Pref.timeSamples = {
0: [(0.14877812564373016, -0.9876883625984192
}
```
Maya Alembic export:

```
custom point3d[] primvars:mtoa_varying_Pref
point3d[] primvars:mtoa_varying_Pref.timeSamples = {
0: [(0.14877812564373016, -0.9876883625984192, -0.
}

```

**Expected behavior**
A clear and concise description of what you expected to happen.

**Screenshots**
If applicable, add screenshots to help explain your problem.

**Used Software Versions**
- Latest Arnold available to me on 15 March 2023

Extract arnold-abc-test.zip and reproduce the issue in Solaris by sublayering the Alembic file, assigning a material, and rendering the test_varying_Pref user data. Compare the Arnold and Maya Alembic USDA output shown in the issue; done means varying-named primvars remain available to the user data shader.

Written by the indexing model from the issue text.