Qt6 migration fixes: RTI DDS alias targets, ErrorMessage namespace, DDS header include path

qt6-after/qt6-migrated-legatus/Lts/Plugins/InfrastructureManagement/ism_data_plugin_interface.h

@@ -4,6 +4,7 @@
 #pragma once
 
 #include <InfrastructureManagement/ism.hpp>
+#include <InfrastructureManagement/ism_mounting_point.h>
 #include <InfrastructureManagement/ism_dtc.h>
 #include <InfrastructureManagement/ism_ftc.h>
 #include <ParticipantManagement/ppm.hpp>
@@ -28,7 +29,6 @@
 namespace InfrastructureManagement
 {
 class ForeignDataInterface;
-class MountingPoint;
 
 // Forward declaration for MainSchedule from ParticipantManagement
 using ParticipantManagement::MainSchedule;