Poll for PowerAppsTestEngine

[landonmsft]

Description

TestEngine needs to poll for the PowerAppsTestEngine global in the web player frame.

Checklist

• [x] The code change is covered by unit tests. I have added tests that prove my fix is effective or that my feature works
• [x] I have performed end-to-end test locally.
• [x] New and existing unit tests pass locally with my changes
• [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
• [x] I used clear names for everything
• [x] I have performed a self-review of my own code

[github-actions[bot]]

Package	Line Rate	Branch Rate	Complexity	Health
Microsoft.PowerApps.TestEngine	93%	91%	766	✔
Summary	93% (2049 / 2197)	91% (469 / 516)	766	✔

Minimum allowed line rate is 50%