Move core and coreimpl from corelib/ to lib/core and lib/coreimpl.

corelib/src/object.dart

-// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-/**
- * Everything in Dart is an [Object].
- */
-class Object {
-  const Object();
-
-  String toString() => ObjectImplementation.toStringImpl(this);
-
-  void noSuchMethod(String name, List args) {
-    ObjectImplementation.noSuchMethodImpl(this, name, args);
-  }
-
-  operator ==(other) => this === other;
-
-  get dynamic() => this;
-}