REVIEW ONLY: Replace 'smart autocomplete' with a purpose-built QuickSearchField module

Simplifies QuickOpen code, removing workarounds and allowing it to use the ModalBar autoClose option. Fixes bugs with arrow key handling, cleans up APIs, and more consistently highlights the item that pressing enter will select.

Fixed issues include: #5871, #3405, #5360, #2757.  I'm _guessing_ this also fixes #5344.

There are still some loose ends to polish up here, including adding unit tests, removing logging code, & catching up with master -- so it's definitely not ready to merge yet.