This aligns Workers and Window and MessagePorts to all use the same
mechanism for transferring serialized messages across realms.
It also allows transferring more message ports into a worker.
Re-enable the Worker-echo test, as none of the MessagePort tests have
themselves been flaky, and those are now using the same underlying
implementation.
NewAKString is effectively the default for any new IDL interface, so
let's mark this as the default behavior. It also makes it much easier to
figure out whatever interfaces are still left to port over to new AK
String.
This initial implementation stubs out the WorkerGlobalScope,
WorkerLocation and WorkerNavigator classes. It doesn't take into account
all the things that actually need passed into the constructors for these
objects, nor the extra abstract operations that need to be performed on
them by the rest of the Browser infrastructure. However, it does create
bindings that compile and link :^)
