Enable PowerApps MDA Gallery Controls for Custom Pages

[v-nabalasubr]

Description

Enable PowerApps MDA Gallery Controls such as Vertical Gallery, Horizontal Gallery, Flexible height Gallery controls for Custom Pages with Test Engine Support. This update involves creating a Power Apps MDA Custom page with Vertical Gallery, Horizontal Gallery, Flexible height Gallery controls for both modern and classic controls and developing a test plan to verify runtime and design time control properties.

Work Items for this PR:
#418 - MDA Modern Gallery Control
#437 - MDA Classic Gallery Control

Checklist

• The code change is covered by unit tests. I have added tests that prove my fix is effective or that my feature works
• I have performed end-to-end test locally.
• New and existing unit tests pass locally with my changes
• 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