Complete Qt6 migration: full clean build green across groups G1-G12 incl. runtime plugin set

new_docker_build.sh gains Group 12 (212 GUI/Data plugins); fixes LtsUtilsGuiDds visibility (LTO-stripped exports), LtsProjectionWorkstation unity name shadow, 6 unity-off dirs (dup file-scope statics, ddsftc INTERFACE sources) and reconfigures BUILD_FILTERMANAGEMENT/BUILD_PLUGINS_SERVICEMONITOR=ON

qt6-after/qt6-migrated-legatus/Lts/Services/ServiceManagement/service_process.cpp

@@ -252,7 +252,7 @@ void ServiceManagement::ServiceProcess::setNewStateFromHeartbeat(const Core::Cur
   m_ports = data.ports;
 
   std::string es;
-  if (data.errorString.is_set())
+  if (data.errorString.has_value())
     es = data.errorString.get();
 
   ServiceInformation info(m_serviceProcessId,