[MAYA-123839] Cannot constrain prims

**Describe the bug**
Constraints (under the Animation menu) do not work with prims. We would like to be able to constrain prims to other prims or native maya nodes.

**Steps to reproduce**
Steps to reproduce the behavior:
1. Open a new file in Maya 2022
2. Navigate to Create -> Polygon Primitives -> Sphere
3. Navigate to Create -> Universal Scene Description (USD) -> Stage with new layer
4. Right click on the proxy shape -> Add new prim -> Capsule
5. Click on the poly sphere (driver) and Shift+Click on USD capsule (driven)
6. Navigate to the Animation menu and open Constrain menu -> Parent

It prints the following error in the script editor:
`// Error: line 0: Target list was empty or contained no valid targets. // `

7. Right click on the proxy shape -> Add new prim -> Cube
8. Click on the USD Cube (driver) and Shift+Click on USD capsule (driven)
9. Navigate to the Animation menu and open Constrain menu -> Parent

It prints the following error in the script editor:
`// Error: line 0: This command requires at least 1 argument(s) to be specified or selected; found 0. // `

**Expected behavior**
We would expect to be able to use Constraint menu items (parent, point, orient, remove target, etc). Would would like to be able to drive usd prims with other usd prims and native maya nodes.

**Specs (if applicable):**
- Linux
- maya2022.update3
- Maya USD commit SHA [dev at 96d3593]
- Pixar USD commit SHA [dev at aaced34]