Change "typedef" to "class" in core library and related tests.

tests/language/mixin_type_parameter1_test.dart

Index: tests/language/mixin_type_parameter1_test.dart
diff --git a/tests/language/mixin_type_parameter1_test.dart b/tests/language/mixin_type_parameter1_test.dart
index d591abd65ee5266a708f937a9f513529d6c9b3fe..3f72898196caa410fbbdbf22f7d3187bacd094a4 100644
--- a/tests/language/mixin_type_parameter1_test.dart
+++ b/tests/language/mixin_type_parameter1_test.dart
@@ -13,7 +13,7 @@ abstract class Mixin2<T> {
 class A {
 }
 
-typedef MyTypedef<K, V> = A with Mixin1<K>, Mixin2<V>;
+class MyTypedef<K, V> = A with Mixin1<K>, Mixin2<V>;
 
 class B<K, V> extends MyTypedef<K, V> {
 }