fix #25578, implement @covariant parameter overrides

pkg/analyzer/lib/src/dart/element/member.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.member;
 
 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 216 matching lines @@
    * Initialize a newly created element to represent a field formal parameter,
    * based on the [baseElement], defined by the [definingType]. If [type]
    * is passed it will be used as the substituted type for this member.
    */
   FieldFormalParameterMember(
       FieldFormalParameterElement baseElement, ParameterizedType definingType,
       [DartType type])
       : super(baseElement, definingType, type);
 
   @override
+  bool get isCovariant => baseElement.isCovariant;
+
+  @override
   FieldElement get field {
     FieldElement field = (baseElement as FieldFormalParameterElement).field;
     if (field is FieldElement) {
       return FieldMember.from(
           field, substituteFor(field.enclosingElement.type));
     }
     return field;
   }
 
   @override
@@ skipping 426 matching lines @@
   @override
   String get defaultValueCode => baseElement.defaultValueCode;
 
   @override
   Element get enclosingElement => baseElement.enclosingElement;
 
   @override
   int get hashCode => baseElement.hashCode;
 
   @override
+  bool get isCovariant => baseElement.isCovariant;
+
+  @override
   bool get isInitializingFormal => baseElement.isInitializingFormal;
 
   @override
   ParameterKind get parameterKind => baseElement.parameterKind;
 
   @override
   List<ParameterElement> get parameters {
     DartType type = this.type;
     if (type is FunctionType) {
       return type.parameters;
@@ skipping 367 matching lines @@
   DartObject computeConstantValue() => baseElement.computeConstantValue();
 
   @override
   void visitChildren(ElementVisitor visitor) {
     // TODO(brianwilkerson) We need to finish implementing the accessors used
     // below so that we can safely invoke them.
     super.visitChildren(visitor);
     baseElement.initializer?.accept(visitor);
   }
 }