Unify the server and plugin versions of the generators

pkg/analyzer_plugin/tool/spec/codegen_matchers.dart

-// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2014, 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.
 
 /**
  * Code generation for the file "matchers.dart".
  */
 import 'dart:convert';
 
 import 'package:analyzer/src/codegen/tools.dart';
 import 'package:front_end/src/codegen/tools.dart';
@@ skipping 167 matching lines @@
     for (TypeDecl choice in typeUnion.choices) {
       if (commaNeeded) {
         write(', ');
       }
       visitTypeDecl(choice);
       commaNeeded = true;
     }
     write('])');
   }
 }