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/Common/LtsTimelineClassic/TimelineIndicator.cpp

@@ -49,7 +49,7 @@ TimelineIndicator::TimelineIndicator(QWidget *parent)
   , m_currentTextWidth(0)
   , m_sectionPos(0)
   , m_sectionSize(0)
-  , m_logger(NGL::NGLLoggerBootstrap::getNGLRootLogger().getNGLLogger("Timeline.Indicator"))
+  .getNGLLogger("Timeline.Indicator"))
 {
   m_timeArray.reserve(11 + 11 + 7 + 10);