UX: Add focus to menu only if it comes from a keyboard shortcut and improve keyboard functionality for search

This removes the focus that was occurring when using a mouse and now only adds it if the keyboard shortcut is used.

This also permits tabbing to work correctly when searching. Up/down bindings have been removed, and now for keyboards tabbing to each result allows them to press enter and get to that search result.

This should help resolve any issues you had with the focus and the highlight.
https://github.com/discourse/discourse/pull/2713