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/DDS/DdsUnitTests/data_topic_tests.cpp

@@ -8,7 +8,7 @@
 #include <DDS/QosProfile/DDS_DefaultQos.h>
 #include <DDS/DTS/generic_dts_impl.h>
 #include <DDS/DTC/generic_dtc_impl.h>
-#include <Common/ProjectConfig/project_defines.h>
+#include <Lts/Common/ProjectConfig/project_defines.h>
 
 #include <QtTest/QTest>
 #include <QVariant>
@@ -26,7 +26,7 @@ DataTopicTests::DataTopicTests()
   , m_subscriberListener(nullptr)
   , m_dtcTestPart(nullptr)
   , m_mainThreadId(QThread::currentThreadId())
-  , m_logger(NGL::NGLLoggerBootstrap::getNGLRootLogger().getNGLLogger("UnitTests.DataTopicTests"))
+  .getNGLLogger("UnitTests.DataTopicTests"))
 {
   if (!DDS::QosProfile::setDefault())
     ERROR_LOG() << "Error setting default QoS from xml-file ";