This is a monster patch that turns all EventTargets into GC-allocated
PlatformObjects. Their C++ wrapper classes are removed, and the LibJS
garbage collector is now responsible for their lifetimes.
There's a fair amount of hacks and band-aids in this patch, and we'll
have a lot of cleanup to do after this.
The WebSocket bindings match the original specification from the
WHATWG living standard, but do not match the later update of the
standard that involves FETCH. The FETCH update will be handled later
since the changes would also affect XMLHttpRequest.
