Improve navigation in the TV demo app

[MGaetan89]

Pull request

Description

This PR improves the navigation in the TV demo app.

Changes made

• When pressing back while on a grid:
  • If the focused item is not on the first row, we give the focus to the first item of the grid, and scroll to it
  • If the focused item is on the first row:
    • If we are on the root screen, we give focus to the top navigation
    • If we are on a nested screen, we navigate back
• Remove some dead code

Checklist

• Your branch has been rebased onto the main branch.
• APIs have been properly documented (if relevant).
• The documentation has been updated (if relevant).
• New unit tests have been written (if relevant).
• The demo has been updated (if relevant).
• All pull request status checks pass.

[StaehliJ]

We could improve top level focus selection. When top level menu is focus, request focus first on the current selected item.

[MGaetan89]

Just a comment on the code, will test the new version now