[EMSUSD-74] Maya Incorrect Framing of unique point instances

Framing a USD instance selection does not properly calculate the extent and places the camera Incorrectly.

**Steps to reproduce**
Steps to reproduce the behavior:
1. Load a point instancer.
2. Set USD selection mode to Instances.
3. Select a sub-section of instances.
4. "F" hotkey to "Fit In View" for the current panel.
6. Observe it is fitting to the entire instancer's bounding box.

**Expected behavior**
The camera to fit to the instance selection directly.

**Attachments**
[bifbro.zip](https://github.com/Autodesk/maya-usd/files/12864656/bifbro.zip)

**Specs (if applicable):**
- Maya version [e.g. Maya 2024]

**Additional context**
Add any other context about the problem here.