Keyboard Focus needs to be updated for when NavigationView displays multi-level items.
Update the focus to no longer be the whole NavigationViewItem in order to allow for navigation down the item tree.

• Update arrow key navigation to behave as expected (XYNavigation)
• Update tab navigation to behave as expected
  • Only tab into the list of menu items once
  • When returning focus via tab or shift-tab, go back to last focused item