Mouse can interact with MRTK UI elements while hands are present in the scene.

[RogPodge]

Describe the bug

When using input simulation, the mouse can accidentally interact with UI elements while the simulated hands are on the screen.

To reproduce

Steps to reproduce the behavior:

1. Open the MRTK HandInteractionExamples scene
2. Start the scene
3. Bring up the simulated hand
4. Try interacting with the scene using the mouse pointer.

Expected behavior

The mouse pointer should be disabled from interacting with elements in the scene when hands are present.

Screenshots

If applicable, add screenshots to help explain your problem.

Your setup (please complete the following information)

• Unity Version 2020.3.36f1
• MRTK Version: 3.0.0-latest