This PR makes selecting a sub-entry in the settings UI nav bar scroll to
that section in the settings page. It also updates the selected
sub-entry when scrolling through a settings page to match what a user is
viewing on the page.

I also added a new helper method to `ScrollHandle` type called
`scroll_to_top_of_item` that scrolls until an item is the top element
visible.

Release Notes:

- N/A