Changed screens for UIManager to use canvas groups instead of canvas

[nicholas-maltbie]

Description

Changed screens to use Canvas Group as opposed to a whole canvas.

This helps with some interactions using the new input system and allow for more future flexibility.

How Has This Been Tested?

This has been tested locally and does not effect existing unit tests using the UI.

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings

[github-actions[bot]]

Test Coverage Results for editmode: Line Coverage: 99.9% Link to run results: https://github.com/nicholas-maltbie/PropHunt-Mirror/actions/runs/966112081

[github-actions[bot]]

Test Coverage Results for playmode: Line Coverage: 27.2% Link to run results: https://github.com/nicholas-maltbie/PropHunt-Mirror/actions/runs/966112081

[github-actions[bot]]

Test Coverage Results for playmode: Line Coverage: 27.2% Link to run results: https://github.com/nicholas-maltbie/PropHunt-Mirror/actions/runs/966148327

[github-actions[bot]]

Test Coverage Results for editmode: Line Coverage: 100% Link to run results: https://github.com/nicholas-maltbie/PropHunt-Mirror/actions/runs/966148327