implement `Invocation.typeArguments` in DDC

tests/language_strong/mock_writable_final_field_test.dart

Index: tests/language_strong/mock_writable_final_field_test.dart
diff --git a/tests/language_strong/mock_writable_final_field_test.dart b/tests/language_strong/mock_writable_final_field_test.dart
index b5c1ff176a6714099cbbc3f95484a219707d1d9b..5a5a164ed181d1e3c2186e5b47dc2b0c45218b73 100644
--- a/tests/language_strong/mock_writable_final_field_test.dart
+++ b/tests/language_strong/mock_writable_final_field_test.dart
@@ -8,7 +8,8 @@ final values = <int>[];
 
 class Mock {
   noSuchMethod(Invocation i) {
-    Expect.equals(i.memberName.toString(), 'Symbol("_x")');
+    var expected = i.isGetter ? "_x" : "_x=";
+    Expect.equals('Symbol("$expected")', i.memberName.toString());
     values.add(i.positionalArguments[0]);
   }
 }