[turbofan] Introduce a dedicated StringCharAt operator.

src/code-factory.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/code-factory.h"
 
 #include "src/bootstrapper.h"
 #include "src/ic/ic.h"
 
 namespace v8 {
@@ skipping 234 matching lines @@
 TFS_BUILTIN(ToLength)
 TFS_BUILTIN(ToObject)
 TFS_BUILTIN(Typeof)
 TFS_BUILTIN(InstanceOf)
 TFS_BUILTIN(OrdinaryHasInstance)
 TFS_BUILTIN(ForInFilter)
 TFS_BUILTIN(NewUnmappedArgumentsElements)
 TFS_BUILTIN(NewRestParameterElements)
 TFS_BUILTIN(PromiseHandleReject)
 TFS_BUILTIN(GetSuperConstructor)
+TFS_BUILTIN(StringCharAt)
 
 #undef TFS_BUILTIN
 
 // static
 Callable CodeFactory::Inc(Isolate* isolate) {
   IncStub stub(isolate);
   return make_callable(stub);
 }
 
 // static
@@ skipping 247 matching lines @@
 }
 
 // static
 Callable CodeFactory::FunctionPrototypeBind(Isolate* isolate) {
   return Callable(isolate->builtins()->FunctionPrototypeBind(),
                   BuiltinDescriptor(isolate));
 }
 
 }  // namespace internal
 }  // namespace v8