Updated docs\PowerFx and added link to SetProperty page

[arpavan]

Description

Updated the Power Fx section of our doc to remove statement indicating "any Power Fx function supported". Also added a link to SetProperty page.

Checklist

• [N/A] The code change is covered by unit tests. I have added tests that prove my fix is effective or that my feature works
• [N/A] I have performed end-to-end test locally.
• [N/A] New and existing unit tests pass locally with my changes
• [N/A] I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I used clear names for everything
• I have performed a self-review of my own code

[github-actions]

Package	Line Rate	Branch Rate	Complexity	Health
Microsoft.PowerApps.TestEngine	91%	88%	925	✔
Summary	91% (2457 / 2686)	88% (559 / 636)	925	✔

Minimum allowed line rate is 85%