Generate constants in server as we do in plugin

pkg/analysis_server/lib/protocol/protocol_generated.dart

 // Copyright (c) 2017, 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.
 //
 // This file has been automatically generated.  Please do not edit it manually.
 // To regenerate the file, use the script
 // "pkg/analysis_server/tool/spec/generate_files".
 
 import 'dart:convert' hide JsonDecoder;
 
@@ skipping 7579 matching lines @@
  * {
  *   "templates": List<PostfixTemplateDescriptor>
  * }
  *
  * Clients may not extend, implement or mix-in this class.
  */
 class EditListPostfixCompletionTemplatesResult implements ResponseResult {
   List<PostfixTemplateDescriptor> _templates;
 
   /**
-   * The list of available template.
+   * The list of available templates.
    */
   List<PostfixTemplateDescriptor> get templates => _templates;
 
   /**
-   * The list of available template.
+   * The list of available templates.
    */
   void set templates(List<PostfixTemplateDescriptor> value) {
     assert(value != null);
     this._templates = value;
   }
 
   EditListPostfixCompletionTemplatesResult(
       List<PostfixTemplateDescriptor> templates) {
     this.templates = templates;
   }
@@ skipping 7106 matching lines @@
     hash = JenkinsSmiHash.combine(hash, classElement.hashCode);
     hash = JenkinsSmiHash.combine(hash, displayName.hashCode);
     hash = JenkinsSmiHash.combine(hash, memberElement.hashCode);
     hash = JenkinsSmiHash.combine(hash, superclass.hashCode);
     hash = JenkinsSmiHash.combine(hash, interfaces.hashCode);
     hash = JenkinsSmiHash.combine(hash, mixins.hashCode);
     hash = JenkinsSmiHash.combine(hash, subclasses.hashCode);
     return JenkinsSmiHash.finish(hash);
   }
 }