Refactor runtime into libraries, better type reps

lib/runtime/dart/core.js

-dart.library('dart/core', null, /* Imports */[
+dart_library.library('dart/core', null, /* Imports */[
+  "dart_runtime/dart"
 ], /* Lazy imports */[
   'dart/_js_helper',
   'dart/_internal',
   'dart/collection',
   'dart/_interceptors',
   'dart/convert'
-], function(exports, _js_helper, _internal, collection, _interceptors, convert) {
+], function(exports, dart, _js_helper, _internal, collection, _interceptors, convert) {
   'use strict';
+  let dartx = dart.dartx;
   class Object {
     constructor() {
       let name = this.constructor.name;
       let init = this[name];
       let result = void 0;
       if (init)
         result = init.apply(this, arguments);
       return result === void 0 ? this : result;
     }
     ['=='](other) {
@@ skipping 3344 matching lines @@
   exports.StackTrace = StackTrace;
   exports.Stopwatch = Stopwatch;
   exports.String = String;
   exports.RuneIterator = RuneIterator;
   exports.StringBuffer = StringBuffer;
   exports.StringSink = StringSink;
   exports.Symbol = Symbol;
   exports.Type = Type;
   exports.Uri = Uri;
 });