Add documentationComment for Class to Kernel. Parse it. Resynthesize in Analyzer.

pkg/analyzer/lib/src/dart/element/element.dart

 // 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.
 
 library analyzer.src.dart.element.element;
 
 import 'dart:collection';
 import 'dart:math' show min;
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 569 matching lines @@
     _assertNotResynthesized(_unlinkedClass);
     assert(!isMixinApplication);
     for (ConstructorElement constructor in constructors) {
       (constructor as ConstructorElementImpl).enclosingElement = this;
     }
     this._constructors = constructors;
   }
 
   @override
   String get documentationComment {
+    if (_kernel != null) {
+      return _kernel.documentationComment;
+    }
     if (_unlinkedClass != null) {
       return _unlinkedClass?.documentationComment?.text;
     }
     return super.documentationComment;
   }
 
   /**
    * Return `true` if [CompileTimeErrorCode.MIXIN_HAS_NO_CONSTRUCTORS] should
    * be reported for this class.
    */
@@ skipping 8400 matching lines @@
 
   @override
   DartObject computeConstantValue() => null;
 
   @override
   void visitChildren(ElementVisitor visitor) {
     super.visitChildren(visitor);
     _initializer?.accept(visitor);
   }
 }