fix #25578, implement @covariant parameter overrides

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

Index: pkg/analyzer/lib/src/dart/element/member.dart
diff --git a/pkg/analyzer/lib/src/dart/element/member.dart b/pkg/analyzer/lib/src/dart/element/member.dart
index 4c95b28e2d80ca569c39633cdb9c2a106cf8cbc3..cf52465ebed7ffa02074fa376c32b8e25d4546a7 100644
--- a/pkg/analyzer/lib/src/dart/element/member.dart
+++ b/pkg/analyzer/lib/src/dart/element/member.dart
@@ -234,6 +234,9 @@ class FieldFormalParameterMember extends ParameterMember
       : super(baseElement, definingType, type);
 
   @override
+  bool get isCovariant => baseElement.isCovariant;
+
+  @override
   FieldElement get field {
     FieldElement field = (baseElement as FieldFormalParameterElement).field;
     if (field is FieldElement) {
@@ -680,6 +683,9 @@ class ParameterMember extends VariableMember
   int get hashCode => baseElement.hashCode;
 
   @override
+  bool get isCovariant => baseElement.isCovariant;
+
+  @override
   bool get isInitializingFormal => baseElement.isInitializingFormal;
 
   @override