[turbofan] Lower StringCharCodeAt to a dedicated builtin.

src/builtins/builtins.h

Index: src/builtins/builtins.h
diff --git a/src/builtins/builtins.h b/src/builtins/builtins.h
index 20d0ce43ce611e94e7b12e85a47b48261fd69d07..5e26a1d311481f650165e383e6b5832a9e3c24cd 100644
--- a/src/builtins/builtins.h
+++ b/src/builtins/builtins.h
@@ -105,6 +105,7 @@ namespace internal {
   TFS(StringGreaterThan, BUILTIN, kNoExtraICState, Compare)                    \
   TFS(StringGreaterThanOrEqual, BUILTIN, kNoExtraICState, Compare)             \
   TFS(StringCharAt, BUILTIN, kNoExtraICState, StringCharAt)                    \
+  TFS(StringCharCodeAt, BUILTIN, kNoExtraICState, StringCharCodeAt)            \
                                                                                \
   /* Interpreter */                                                            \
   ASM(InterpreterEntryTrampoline)                                              \