Utils: Send ack from Process stub

Allow the server to listen for command results.
Fixes Qt Creator hanging when stopping application
being debugged.

Change-Id: Ia175b1bb1836b5593bc073394fa152923e1dda28
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Cristian Adam <cristian.adam@qt.io>

src/tools/process_stub/main.cpp

@@ -542,6 +542,8 @@ void onControlSocketReadyRead()
             break;
         }
         }
+
+        sendMsg(QString("ack %1\n").arg(ch).toUtf8());
     }
 }