Migrate some case conversion functions from JS to CPP builtins

src/builtins/builtins.h

Index: src/builtins/builtins.h
diff --git a/src/builtins/builtins.h b/src/builtins/builtins.h
index 902cd8dbfbee28da32f290b89cdc1329e840339d..f9d892861a0a01010cc9d654a6037555915047e4 100644
--- a/src/builtins/builtins.h
+++ b/src/builtins/builtins.h
@@ -771,14 +771,19 @@ class Isolate;
   CPP(StringPrototypeStartsWith)                                               \
   /* ES6 section 21.1.3.25 String.prototype.toString () */                     \
   TFJ(StringPrototypeToString, 0)                                              \
-  /* ES #sec-string.prototype.tolocalelowercase */                             \
+  /* (obsolete) Unibrow string functions */                                    \
   CPP(StringPrototypeToLocaleLowerCase)                                        \
-  /* ES #sec-string.prototype.tolocaleuppercase */                             \
   CPP(StringPrototypeToLocaleUpperCase)                                        \
-  /* ES #sec-string.prototype.tolowercase */                                   \
   CPP(StringPrototypeToLowerCase)                                              \
-  /* ES #sec-string.prototype.touppercase */                                   \
   CPP(StringPrototypeToUpperCase)                                              \
+  /* ES #sec-string.prototype.tolocalelowercase */                             \
+  /* CPP(StringPrototypeToLocaleLowerCaseI18N) */                              \
+  /* ES #sec-string.prototype.tolocaleuppercase */                             \
+  /* CPP(StringPrototypeToLocaleUpperCaseI18N) */                              \
+  /* ES #sec-string.prototype.tolowercase */                                   \
+  CPP(StringPrototypeToLowerCaseI18N)                                          \
+  /* ES #sec-string.prototype.touppercase */                                   \
+  CPP(StringPrototypeToUpperCaseI18N)                                          \
   CPP(StringPrototypeTrim)                                                     \
   CPP(StringPrototypeTrimLeft)                                                 \
   CPP(StringPrototypeTrimRight)                                                \