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 :^)
It's very common to encounter single-character strings in JavaScript on
the web. We can make such strings significantly lighter by having a
1-character inline capacity on the Vectors.
The current method of iterating through the string to access a code
point hurts performance quite badly for very large strings. The test262
test "RegExp/property-escapes/generated/Any.js" previously took 3 hours
to complete; this one change brings it down to under 10 seconds.
To be used as a RegexStringView variant, Utf16View must provide a couple
more helper methods. It must also not default its assignment operators,
because that implicitly deletes move/copy constructors.
