Complete PrtCnv Qt6 migration so CoPrtCnv/PrtCnvLib/PrtCnv/ddsview build

Restore dropped m_logger members, QMutex->QRecursiveMutex, splitView->split, error->errorOccurred (migration-only, verified vs legacy).

qt6-after/qt6-migrated-legatus/TetraIF/PrtCnv/TetraTestServer/worker.cpp

@@ -30,7 +30,7 @@ bool TTWorker::init()
 {
   connect(m_socket, &QTcpSocket::disconnected,
           this, &TTWorker::deleteLater);
-  connect(m_socket, QOverload<QAbstractSocket::SocketError>::of(&QTcpSocket::error),
+  connect(m_socket, &QAbstractSocket::errorOccurred,
           this, &TTWorker::onSocketError);
   connect(m_socket, &QTcpSocket::readyRead,
           this, &TTWorker::onReadyRead);