Modify GetPropertyValue expression to align with BuildObjectModel

[clairewu0218]

Pull Request Template

Description

Modify GetPropertyValue expression for the purpose of:

1. Stringify the return value on the Test Engine side. Align with how buildObjectModel works to avoid confusion.
2. Align with the OnePlayer JSSDK

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%	764	✔
Summary	93% (2032 / 2176)	91% (471 / 518)	764	✔

Minimum allowed line rate is 50%