The ManipMoveContext class of commands don't work on Usd Xforms

The ManipMoveContext class of commands don't work on Usd Xforms.
Pre and post drag commands never get fired off.

Steps to reproduce the behavior:
1. Create a usd xform
2. Run this python snippet to hook up the preDragCommand
```
def testFunc():
print("Drag Initiated")
cmds.manipMoveContext('Move', e=True, preDragCommand=[testFunc, "Xform"])
```
3. Deselect all
4. Move the Xform, the preDragCommand does not fire off

**Expected behavior**
The preDragCommand should be called when the manipulator is dragged, as it does for a regular maya transform.

**Specs (if applicable):**
- Windows 10
- Maya 2022
- MayaUsd Version 0.18.0
- Usd Version 21.11