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 :^)
Instead of just keeping them in an unsorted Vector, which led to
increasingly noticeable O(n) lookups, we now cache a list of Typefaces
per family name.
Also make the font discovery algorithm search subdirectories as well.
This will be used by Ladybird to discover more fonts on non-Serenity
systems. :^)
