Note that js_rope_string() has been folded into this, the old name was
misleading - it would not always create a rope string, only if both
sides are not empty strings. Use a three-argument create() overload
instead.
This will make it easier to support both string types at the same time
while we convert code, and tracking down remaining uses.
One big exception is Value::to_string() in LibJS, where the name is
dictated by the ToString AO.
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 matches the Infra spec's definition of 'ASCII whitespace', and we
can at last stop using AK::is_ascii_space(), which has a different idea
about what 'whitespace' means.
Usually operations that mirror AOs from the Infra spec are simply part
of the underlying data structures in AK directly, but these don't seem
generally useful enough to add them as ByteBuffer methods.
