Elements. Change ExecutableElementOrMember.typeParameters to return List<TypeParameterElementImpl>.

Change-Id: I9527e21fcc7caf58f4b42a929d302c8423273628
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/417081
Reviewed-by: Paul Berry <[email protected]>
Commit-Queue: Konstantin Shcheglov <[email protected]>

Author: scheglov

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

@@ -8,7 +8,6 @@ import 'package:analyzer/dart/element/element2.dart';
 import 'package:analyzer/dart/element/nullability_suffix.dart';
 import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/src/dart/element/element.dart';
-import 'package:analyzer/src/dart/element/member.dart';
 import 'package:analyzer/src/dart/element/type.dart';
 import 'package:analyzer/src/dart/element/type_algebra.dart';
 import 'package:analyzer/src/utilities/extensions/element.dart';
@@ -127,10 +126,7 @@ class ElementDisplayStringBuilder {
     _write(name);
 
     if (element.kind != ElementKind.GETTER) {
-      var typeParameters = (element is ExecutableElementImpl)
-          ? element.typeParameters
-          : (element as ExecutableMember).typeParameters;
-      _writeTypeParameters(typeParameters);
+      _writeTypeParameters(element.typeParameters);
       _writeFormalParameters(
         element.parameters,
         forElement: true,

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

@@ -3839,6 +3839,9 @@ abstract class ExecutableElementOrMember
 
   @override
   FunctionTypeImpl get type;
+
+  @override
+  List<TypeParameterElementImpl> get typeParameters;
 }
 
 /// A concrete implementation of an [ExtensionElement].