fix #25578, implement @covariant parameter overrides

pkg/analyzer/lib/src/dart/element/handle.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.generated.element_handle;
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/constant/value.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
@@ skipping 887 matching lines @@
       ElementResynthesizer resynthesizer, ElementLocation location)
       : super(resynthesizer, location);
 
   @override
   ParameterElement get actualElement => super.actualElement as ParameterElement;
 
   @override
   String get defaultValueCode => actualElement.defaultValueCode;
 
   @override
+  bool get isCovariant => actualElement.isCovariant;
+
+  @override
   bool get isInitializingFormal => actualElement.isInitializingFormal;
 
   @override
   ElementKind get kind => ElementKind.PARAMETER;
 
   @override
   ParameterKind get parameterKind => actualElement.parameterKind;
 
   @override
   List<ParameterElement> get parameters => actualElement.parameters;
@@ skipping 201 matching lines @@
 
   @override
   bool get isStatic => actualElement.isStatic;
 
   @override
   DartType get type => actualElement.type;
 
   @override
   DartObject computeConstantValue() => actualElement.computeConstantValue();
 }