Add worker_threads interop file and implementation

Something here is not working 100%, on running render `ParentPort` is null and it should be an object if its on the worker thread.

Author: hegelocampus

lib/src/node.dart

@@ -80,7 +80,6 @@ Future<RenderResult> _renderAsync(RenderOptions options) async {
   var start = DateTime.now();
   var file = options.file == null ? null : p.absolute(options.file);
   CompileResult result;
-
   if (isMainThread == true) {
     print("Creating worker thread");
     final worker = Worker(p.current, WorkerOptions(workerData: {options}));

lib/src/node/worker_threads.dart

@@ -1,6 +1,9 @@
 // Copyright 2020 Google Inc. Use of this source code is governed by an
 // MIT-style license that can be found in the LICENSE file or at
 // https://opensource.org/licenses/MIT.
+@JS()
+library worker_threads;
+
 import 'package:js/js.dart';
 
 @JS("worker_threads")