This produces a (truly) null DeprecatedString, which is not expected to
occur by CharacterData (where this string ends up).
Simply pass an "empty" DeprecatedString manually instead.
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 :^)
