ShaderPort::getPath() should be parented at surfacematerial

Consider the following material document
```

```
`USD_PlasticOne` and `USD_PlasticTwo` are two valid shaders. However, when we use the shader reflection

`MaterialX::ShaderPort::getPath()` will report `SR_plastic/diffuseColor` for both `surfacematerial`

Additional details on slack [here](https://academysoftwarefdn.slack.com/archives/C0230LWBE2X/p1693526751416309)

Start at ShaderPort::getPath() in the shader-reflection code and reproduce the supplied material document. Compare the paths for USD_PlasticOne and USD_PlasticTwo, then verify that each includes its surfacematerial parent rather than only SR_plastic. Done means the two valid materials produce distinct, correctly parented paths.

Written by the indexing model from the issue text.