Merge feature/qt6-migration-basis-modules-services into feature/qt6-migration-basis-modules

Resolves 17 conflicts against legacy Qt5 semantics; validates with BUILD_RTI=ON BUILD_GRANTLEE=ON.

qt6-after/qt6-migrated-legatus/.forward-declarations/include/AdlerJson/interface_controller.h

@@ -0,0 +1,15 @@
+#pragma once
+
+class InterfaceController
+{
+public:
+  InterfaceController();
+
+public Q_SLOTS:
+  void onRegistration();
+  void onDeregistration();
+
+  void onNewConnection();
+  void onWebSocketDisconnected();
+  void onTextMessageReceived(const QByteArray &baJson);
+};