Implemented StartAdvertising() API for Dart Wrappers.

PiperOrigin-RevId: 404088232

windows/dart/core_adapter_dart.cc

@@ -162,7 +162,6 @@ void StartAdvertisingDart(Core* pCore,
                                    "Posting message to port failed.");
                       }
                     };
-
     ResultCallback callback;
     callback.result_cb = [result_cb](Status status) {
       NEARBY_LOG(INFO, "Result callback called. %d.", status.value);

windows/dart/core_adapter_dart.h

@@ -65,7 +65,6 @@ DLL_API void __stdcall StartAdvertisingDart(Core* pCore,
                                       Dart_Port disconnected_cb,
                                       Dart_Port bandwidth_changed_cb,
                                       Dart_Port result_cb);
-
 // Stops advertising a local endpoint. Should be called after calling
 // StartAdvertising, as soon as the application no longer needs to advertise
 // itself or goes inactive. Payloads can still be sent to connected