Upgrade PowerFx.Interpreter library to 0.2.6-preview

[arpavan]

Description

This PR upgrades the version of Microsoft.PowerFx.Interpreter to 0.2.6-preview, and addresses any compile time and breaking changes and also updates tests associated with this upgrade.

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	91%	88%	925	✔
Summary	91% (2457 / 2686)	88% (559 / 636)	925	✔

Minimum allowed line rate is 85%