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/resource_path.cpp

@@ -0,0 +1,51 @@
+/**
+  * @RDE_HEADER@
+  * Helper function to get the resource path
+  * $Id$
+  * $HeadURL$
+  * $Author$
+  */
+
+
+#include "resource_path.h"
+
+
+#include <ngltools/ngltools_filesystem.h> // for NGL::directories
+
+
+// Qt
+#include <QDir>
+#include <QVector>
+
+
+//----------------------------------------------------------------------------
+namespace SituationMap
+{
+
+
+QString getResourcePath()
+{
+  const QString resDir = NGL::directory(NGL::FileType::ConfigFile, QLatin1String("resources"));
+  if (!resDir.isEmpty())
+    return resDir;
+
+  QVector<QString> pathsToSearch;
+
+  // for old systems
+#ifdef Q_OS_WIN
+  pathsToSearch += QLatin1String("C:/ExtFw/resources/");
+#else
+  pathsToSearch += QLatin1String("/usr/share/arcgis/resources");
+#endif
+
+  for (const QString &path : qAsConst(pathsToSearch))
+  {
+    if (QDir(path).exists())
+      return path + QLatin1Char('/');
+  }
+  return QString();
+}
+
+
+} // namespace SituationMap
+