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 :^)
Users can now determine whether a thread has been started or not. A
started thread might also have already terminated.
Implementation note: We *could* detect this with pthread APIs maybe, but
this is much simpler.
While null StringViews are just as bad, these prevent the removal of
StringView(char const*) as that constructor accepts a nullptr.
No functional changes.
Sometimes you don't care about `joining()` the result of a thread. The
underlying pthread implementation already existed for detaching and
now we expose it to the higher level API.
