[builtins] migrate C++ String Iterator builtins to baseline TurboFan

src/builtins/builtins.h

Index: src/builtins/builtins.h
diff --git a/src/builtins/builtins.h b/src/builtins/builtins.h
index aba947beffacff396d475614108be55df734a993..ad803d27f8a16aadd1220ab81b068882f4b13111 100644
--- a/src/builtins/builtins.h
+++ b/src/builtins/builtins.h
@@ -553,10 +553,10 @@ namespace internal {
   /* ES6 section 21.1.3.28 String.prototype.valueOf () */                     \
   TFJ(StringPrototypeValueOf, 1)                                              \
   /* ES6 #sec-string.prototype-@@iterator */                                  \
-  CPP(StringPrototypeIterator)                                                \
+  TFJ(StringPrototypeIterator, 1)                                             \
                                                                               \
   /* StringIterator */                                                        \
-  CPP(StringIteratorPrototypeNext)                                            \
+  TFJ(StringIteratorPrototypeNext, 1)                                         \
                                                                               \
   /* Symbol */                                                                \
   CPP(SymbolConstructor)                                                      \