* Add regex & case-sensitive toggle buttons to Find/Replace UI instead of
deciding based on heuristics. (NOT changed in Find in Files yet, though)
* Change Find Next to use editor cursor pos rather than an invisible saved
pos (part of future story "Correct Find Next behavior", but also simplifies
code). With simple unit test.
* Make all Find/Replace buttons non-tabbable for now, to match existing
next/prev buttons
* Move Find in Files "no results" message back into search bar (as opposed
to drop-down error popup)
* Hide regexp error popup when sliding out Find in Files bar, just as we
do for Find/Replace
* Fix existing bug in Find in Files where prepopulated regexp text was not
checked for errors