[Tizen] CollectionView optimize for TV profile

[myroot]

Description of Change

• This PR optimize CollectionView for TV profile
  • ScrollStep of CollectionView was increased to item size, it improve scrolling of items
  • Focused items was raised to the top, it fix focus effect issue on some apps
  • VisibleItemIndex on Scrolled event was not correct with header/footer, it was fixed
  • Add FocusedItemScrollPosition property in ItemsView as TizenSpecific, useful for controlling with focus.

Issues Resolved

• fixes #

API Changes

Added:

public static void Xamarin.Forms.PlatformConfiguration.TizenSpecific.ItemsView.SetFocusedItemScrollPosition(BindableObject element, ScrollToPosition position)
public static ScrollToPosition Xamarin.Forms.PlatformConfiguration.TizenSpecific.ItemsView.GetFocusedItemScrollPosition(BindableObject element)

Platforms Affected

• Tizen

Behavioral/Visual Changes

None

Before/After Screenshots

• FocusedItemScrollPosition
  

Testing Procedure

PR Checklist

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