Support FormData outside Window scopes.
Add newlines in global.rs.
Implement a stub Worker interface.

Part of #2811.
Implement stub classes for WorkerGlobalScope and DedicatedWorkerGlobalScope.

Part of #2811.
more-globals
Parse the URL passed to the Worker constructor.
Spawn a thread.
Add a constructor for DedicatedWorkerGlobalScope.
Load scripts.
jscontext
Console.