[element model] migrate return_type_verifier

Change-Id: I8cdfd528bee381a2288ff739aec36f1b63bbfe61
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/395085
Auto-Submit: Phil Quitslund <[email protected]>
Commit-Queue: Phil Quitslund <[email protected]>
Commit-Queue: Konstantin Shcheglov <[email protected]>
Reviewed-by: Konstantin Shcheglov <[email protected]>

Author: pq

pkg/analyzer/analyzer_use_new_elements.txt

@@ -119,7 +119,6 @@ lib/src/error/nullable_dereference_verifier.dart
 lib/src/error/override_verifier.dart
 lib/src/error/redeclare_verifier.dart
 lib/src/error/required_parameters_verifier.dart
-lib/src/error/return_type_verifier.dart
 lib/src/error/super_formal_parameters_verifier.dart
 lib/src/error/type_arguments_verifier.dart
 lib/src/error/unused_local_elements_verifier.dart

pkg/analyzer/lib/src/error/return_type_verifier.dart

@@ -3,7 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:analyzer/dart/ast/ast.dart';
-import 'package:analyzer/dart/element/element.dart';
+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/error/listener.dart';
@@ -83,7 +83,7 @@ class ReturnTypeVerifier {
     }
 
     void checkElement(
-      ClassElement expectedElement,
+      ClassElement2 expectedElement,
       AnalyzerErrorCode errorCode,
     ) {
       void reportError() {
@@ -112,18 +112,18 @@ class ReturnTypeVerifier {
     if (enclosingExecutable.isAsynchronous) {
       if (enclosingExecutable.isGenerator) {
         checkElement(
-          _typeProvider.streamElement,
+          _typeProvider.streamElement2,
           CompileTimeErrorCode.ILLEGAL_ASYNC_GENERATOR_RETURN_TYPE,
         );
       } else {
         checkElement(
-          _typeProvider.futureElement,
+          _typeProvider.futureElement2,
           CompileTimeErrorCode.ILLEGAL_ASYNC_RETURN_TYPE,
         );
       }
     } else if (enclosingExecutable.isGenerator) {
       checkElement(
-        _typeProvider.iterableElement,
+        _typeProvider.iterableElement2,
         CompileTimeErrorCode.ILLEGAL_SYNC_GENERATOR_RETURN_TYPE,
       );
     }
@@ -294,7 +294,7 @@ class ReturnTypeVerifier {
     );
   }
 
-  bool _isLegalReturnType(ClassElement expectedElement) {
+  bool _isLegalReturnType(ClassElement2 expectedElement) {
     DartType returnType = enclosingExecutable.returnType;
     //
     // When checking an async/sync*/async* method, we know the exact type