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/Plugins/InfrastructureManagement/ism_data_plugin_interface.h

@@ -3,9 +3,11 @@
 
 #pragma once
 
+#include <InfrastructureManagement/ism.hpp>
+#include <InfrastructureManagement/ism_dtc.h>
+#include <InfrastructureManagement/ism_ftc.h>
 #include <ParticipantManagement/ppm.hpp>
-#include <Services/InfrastructureManagement/ism_dtc.h>
-#include <Services/InfrastructureManagement/ism_ftc.h>
+#include <Services/AreaEffectSimulation/aes.hpp>
 
 #include <QObject>
 #include <QSet>
@@ -28,7 +30,8 @@ namespace InfrastructureManagement
 class ForeignDataInterface;
 class MountingPoint;
 
-
+// Forward declaration for MainSchedule from ParticipantManagement
+using ParticipantManagement::MainSchedule;
 
 
 class ISMDATAPLUGININTERFACE_EXPORT DataInterface : public DataPluginBase::Interface