Fix FlyoutItem recycling

[PureWeen]

Description of Change

Currently on iOS and Android when you scroll the Flyout the Flyout Items will clear and recreate renderers. They will also clear and recreate renderers if you remove items or rearrange. This causes a lot of churn. This PR disables cell recycling on iOS and Android since we're not dealing with massive lists. If users want full virtualization for the FlyoutItems they should use a custom FlyoutContent with a CollectionView. These changes also keep track of FlyoutItems so when the list is modified that cells/renderers are reused instead of recreating everything.

These changes are optimized around a small to medium sized list

Platforms Affected

• iOS
• Android

Testing Procedure

• make sure the store shell flyout scrolls nicely
• Test a few of the UI tests that involve flyout visibility to make sure items show and vanish

PR Checklist

• Targets the correct branch
• Tests are passing (or failures are unrelated)

[PureWeen]

Failing Tests not related

[rmarinho]

@PureWeen works great, the first scroll is slow (it was also before), but then after that it butter smooth..