Improve navigation bar in the TV demo app

[MGaetan89]

Pull request

Description

While working on #293, I discovered that there is already a component for TV to highlight an active item. So the goal of this PR is to simplify some of the changes made in #294.

Changes made

• Simplify MainActivity by removing redundant nested Boxes and use a Column instead
• Add previews to newly created components
• Simplify TVDemoTopBar by using existing native components

Screenshots

New top bar with focus on the first element:

New top bar without focus and first element selected:

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.

[defagos]

Nice find!