BUILD_RTI conditional fixes and Qt6 API updates

- cmake/FindRTI.cmake: Add INTERFACE placeholder targets when RTI not found
- cmake/FindRTI.cmake: Force BUILD_RTI=OFF when RTI not installed
- Lts/Common/LtsSession/CMakeLists.txt: Make LtsSessionDataDds conditional on BUILD_RTI
- Lts/Viewer/CMakeLists.txt: Make LtsDataView conditional on BUILD_RTI
- Lts/Plugins/*/CMakeLists.txt: 97 plugin files wrapped in BUILD_RTI conditionals
- cmake/NGLMacros.cmake: Fix NGL_ADD_BIG_RESOURCES macro (removed premature return())
- Multiple Qt6 API fixes: QLinkedList→std::list, QStringRef→QStringView, etc.
- BUILD_RTI_FIXES_SUMMARY.md: Comprehensive documentation of all fixes

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

qt6-after/qt6-migrated-legatus/Lts/Viewer/SituationMap/Common/referenced.cpp

@@ -0,0 +1,76 @@
+/**
+**
+** @RDE_HEADER@
+** Base class for reference counted objects
+** $Id$
+** $HeadURL$
+** $Author$
+**
+** -----------------------------------------------------------------------------------------------
+**
+** Hardware-Umgebung: Intel-PC
+** Software-Umgebung: Linux, Windows 7, Qt 5.4. ArcGIS 10.2.5
+**
+** Pgrm-Sprache ....: C++ 11
+**
+** HIER/SACHN ......: P: -- ---- - --- QE
+**
+** Version .........: $Revision$
+** -----------------------------------------------------------------------------------------------
+**
+** Autor ...........: Nikolaus Hanekamp, SEDG, Tel. 2906
+**                    Joerg Turla, SPD G, Tel. 3132
+**
+** -----------------------------------------------------------------------------------------------
+**
+** Notizen .........:
+**
+**   18.08.2004, NH  : Urversion
+**   13.05.2015, JT  : Refactoring for use with Qt5, ArcGIS 10.2.5
+**
+** -----------------------------------------------------------------------------------------------
+*/
+
+
+#include "referenced.h"
+
+#include <QDebug>
+
+#include <typeinfo>
+#include <memory>
+
+
+namespace SituationMap
+{
+
+std::shared_ptr<DeleteHandler> & s_deleteHandler()
+{
+  static std::shared_ptr<DeleteHandler> deleteHandler(nullptr);
+  return deleteHandler;
+} // std::shared_ptr<DeleteHandler> & s_deleteHandler()
+
+
+void Referenced::setDeleteHandler(DeleteHandler *handler)
+{
+  s_deleteHandler().reset(handler);
+} // Referenced::setDeleteHandler
+
+
+DeleteHandler *Referenced::getDeleteHandler() { return s_deleteHandler().get(); }
+
+
+Referenced::~Referenced()
+{
+  if (_refCount > 0)
+  {
+    qCritical() << "Deleting still referenced object < " << QString::number((qint64)this, 0, 16) << ">"
+                <<  "of type <" << typeid(this).name() << ">"
+                <<  "refCnt: <" << _refCount;
+
+  }
+} // Referenced::~Referenced
+
+} // end of namespace SituationMap
+
+
+