This adds support for WebSocket subprotocols to WebSocket DOM
objects, with some necessary plumbing to LibWebSocket and its
clients.
See the associated pull request for how this was tested.
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 :^)
The WebSocket service isolates communication with a WebSocket to its
own isolated process. Similar to other isolating services, it has its
own user and group.
