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 4c3749924ca709a5d4c6998d8c4744f8d3fbbb3c..b9508032f303e2594666ac27e9a59a7b794e72fb 100644
--- a/pkg/analyzer/lib/src/dart/element/type.dart
+++ b/pkg/analyzer/lib/src/dart/element/type.dart
@@ -1381,6 +1381,15 @@ 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