We have a new, improved string type coming up in AK (OOM aware, no null
state), and while it's going to use UTF-8, the name UTF8String is a
mouthful - so let's free up the String name by renaming the existing
class.
Making the old one have an annoying name will hopefully also help with
quick adoption :^)
Compared to traditional modal search, incremental search begins
matching as soon as the user starts typing, highlighting results
immediately. This refactors Itamar's work for HackStudio into a
common LibGUI widget to be used in all multi-line TextEditors.
