Complete Qt6 migration: full clean build green across groups G1-G12 incl. runtime plugin set

new_docker_build.sh gains Group 12 (212 GUI/Data plugins); fixes LtsUtilsGuiDds visibility (LTO-stripped exports), LtsProjectionWorkstation unity name shadow, 6 unity-off dirs (dup file-scope statics, ddsftc INTERFACE sources) and reconfigures BUILD_FILTERMANAGEMENT/BUILD_PLUGINS_SERVICEMONITOR=ON

qt6-after/qt6-migrated-legatus/Lts/DDS/Generic/generic_data_writer.h

@@ -86,7 +86,7 @@ template <typename TOPICTYPE> class GenericDataWriter final
             return false;
         }
 
-        if (si.is_set())
+        if (si.has_value())
         {
             rti::pub::WriteParams writeParams;
             rti::core::SampleIdentity sampleIdentity(si.get()->source_guid(), si.get()->publication_sequence_number());