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 :^)
The implementation of `rev` found on Linux systems does not have this
behavior, however other utilities do offer this behavior and so there
really isn't too much of an argument to be made for *not* having this as
a feature.
