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

corelib/src/implementation/options.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.
-
-class RuntimeOptions implements Options {
-  List<String> get arguments() {
-    if (_arguments === null) {
-      // On first access make a copy of the native arguments.
-      _arguments = _nativeArguments.getRange(0, _nativeArguments.length);
-    }
-    return _arguments;
-  }
-
-  String get executable() {
-    return _nativeExecutable;
-  }
-
-  String get script() {
-    return _nativeScript;
-  }
-
-  List<String> _arguments = null;
-
-  // This arguments singleton is written to by the embedder if applicable.
-  static List<String> _nativeArguments = const [];
-
-  // This executable singleton is written to by the embedder if applicable.
-  static String _nativeExecutable = '';
-
-  // This script singleton is written to by the embedder if applicable.
-  static String _nativeScript = '';
-}