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

test/mjsunit/es6/string-iterator.js

Index: test/mjsunit/es6/string-iterator.js
diff --git a/test/mjsunit/es6/string-iterator.js b/test/mjsunit/es6/string-iterator.js
index 8eb27b199aac6a81cc4c81276e1de2428cb2524e..b63de36fc55d37070ad06f5615bcdb1aa7cf0003 100644
--- a/test/mjsunit/es6/string-iterator.js
+++ b/test/mjsunit/es6/string-iterator.js
@@ -92,3 +92,11 @@ function TestNonOwnSlots() {
   assertThrows(function() { object.next(); }, TypeError);
 }
 TestNonOwnSlots();
+
+
+function TestSlicedStringRegression() {
+  var long_string = "abcdefhijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
+  var sliced_string = long_string.substring(1);
+  var iterator = sliced_string[Symbol.iterator]();
+}
+TestSlicedStringRegression();