src: elide heap allocation in structured clone implementation

Small perf improvement:

    $ node benchmark/compare.js --runs 100 \
    >   --old ./node-0da120f879 --new ./node \
    >   --filter structured-clone misc > comparison.csv && \
    >   npx node-benchmark-compare comparison.csv

    [00:02:15|% 100| 1/1 files | 200/200 runs | 3/3 configs]: Done
                                                        confidence improvement accuracy (*)   (**)  (***)
    misc/structured-clone.js n=10000 type='arraybuffer'         **      1.81 %       ±1.28% ±1.68% ±2.16%
    misc/structured-clone.js n=10000 type='object'               *      0.62 %       ±0.55% ±0.73% ±0.93%
    misc/structured-clone.js n=10000 type='string'             ***      8.30 %       ±1.46% ±1.92% ±2.47%

    Be aware that when doing many comparisons the risk of a false-positive result increases.
    In this case, there are 3 comparisons, you can thus expect the following amount of false-positive results:
      0.15 false positives, when considering a   5% risk acceptance (*, **, ***),
      0.03 false positives, when considering a   1% risk acceptance (**, ***),
      0.00 false positives, when considering a 0.1% risk acceptance (***)

PR-URL: #61703
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>

Author: addaleax

src/node_messaging.cc

@@ -1606,11 +1606,11 @@ static void StructuredClone(const FunctionCallbackInfo<Value>& args) {
     }
   }
 
-  std::shared_ptr<Message> msg = std::make_shared<Message>();
+  Message msg;
   Local<Value> result;
-  if (msg->Serialize(env, context, value, transfer_list, Local<Object>())
+  if (msg.Serialize(env, context, value, transfer_list, Local<Object>())
           .IsNothing() ||
-      !msg->Deserialize(env, context, nullptr).ToLocal(&result)) {
+      !msg.Deserialize(env, context, nullptr).ToLocal(&result)) {
     return;
   }
   args.GetReturnValue().Set(result);