fix #28008, fix #28009 implement FutureOr<T>

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

Index: pkg/analyzer/lib/src/dart/element/type.dart
diff --git a/pkg/analyzer/lib/src/dart/element/type.dart b/pkg/analyzer/lib/src/dart/element/type.dart
index dab72dcd6a70cc0dc0a8eb023013f18297cc3e36..253bf99b3903b4fef1792006d237df9fa3eef610 100644
--- a/pkg/analyzer/lib/src/dart/element/type.dart
+++ b/pkg/analyzer/lib/src/dart/element/type.dart
@@ -1387,6 +1387,15 @@ class InterfaceTypeImpl extends TypeImpl implements InterfaceType {
   }
 
   @override
+  bool get isDartAsyncFutureOr {
+    ClassElement element = this.element;
+    if (element == null) {
+      return false;
+    }
+    return element.name == "FutureOr" && element.library.isDartAsync;
+  }
+
+  @override
   bool get isDartCoreFunction {
     ClassElement element = this.element;
     if (element == null) {
@@ -2377,6 +2386,9 @@ abstract class TypeImpl implements DartType {
   bool get isDartAsyncFuture => false;
 
   @override
+  bool get isDartAsyncFutureOr => false;
+
+  @override
   bool get isDartCoreFunction => false;
 
   @override