* Use regex/case toggle buttons to Find in Files UI also
* Persist regex/case toggle state as a pref (shared across Find, Replace &
Find in Files)
* Unit tests for new Sprint 35 find/replace features
* Replace keyboard shortcut acts like clicking the Replace button while
search bar is open
* Show keyboard shortcuts in search bar tooltips
* UI polish: make regex/case option snug with search field; make replace
buttons snug with replace field; don't overlap borders of snug buttons
(caused border to appear darker when disabled due to alpha)