Copy files for splitting src/compiler.dart into several libraries

pkg/compiler/lib/src/diagnostics/spannable.dart

 // Copyright (c) 2011, 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.
 
 library dart2js.util;
 
 import 'util_implementation.dart';
 import 'characters.dart';
 
 export 'setlet.dart';
@@ skipping 242 matching lines @@
   if (usedNames.contains(suggestedName)) {
     int counter = 0;
     while (usedNames.contains(result)) {
       counter++;
       result = "$suggestedName$counter";
     }
   }
   usedNames.add(result);
   return result;
 }