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 :^)
This is an editorial change in the Intl spec:
7c13db4
This also normalizes the spelling of the "Internal slots" heading in
Intl.Collator, which is another editorial change in the Intl spec:
ec064bd
