treat void as a top type, analyzer fix for #28763

pkg/analyzer/test/src/task/strong/checker_test.dart

Index: pkg/analyzer/test/src/task/strong/checker_test.dart
diff --git a/pkg/analyzer/test/src/task/strong/checker_test.dart b/pkg/analyzer/test/src/task/strong/checker_test.dart
index fcd68a9f5ba4864873402b5bbad81adcd6d8475f..83905c60cb4e66b0b36d3f0d93dec872240259b3 100644
--- a/pkg/analyzer/test/src/task/strong/checker_test.dart
+++ b/pkg/analyzer/test/src/task/strong/checker_test.dart
@@ -3502,7 +3502,7 @@ class A {
   void set d(y) => voidFn();
   /*warning:NON_VOID_RETURN_FOR_SETTER*/int set e(y) => 4;
   /*warning:NON_VOID_RETURN_FOR_SETTER*/int set f(y) =>
-      /*error:RETURN_OF_INVALID_TYPE*/voidFn();
+      /*info:DOWN_CAST_IMPLICIT*/voidFn();
   set g(y) {return /*error:RETURN_OF_INVALID_TYPE*/4;}
   void set h(y) {return /*error:RETURN_OF_INVALID_TYPE*/4;}
   /*warning:NON_VOID_RETURN_FOR_SETTER*/int set i(y) {return 4;}
@@ -4147,7 +4147,7 @@ class B extends A {
 typedef int Foo();
 void foo() {}
 void main () {
-  Foo x = /*error:INVALID_ASSIGNMENT,info:USE_OF_VOID_RESULT*/foo();
+  Foo x = /*warning:DOWN_CAST_COMPOSITE,info:USE_OF_VOID_RESULT*/foo();
 }
 ''');
   }