[cpp-qt-client]Prefix signal argument types with namespace

For reason see: https://github.com/KDE/clazy/blob/master/docs/checks/README-fully-qualified-moc-types.md

Author: martonmiklos

modules/openapi-generator/src/main/resources/cpp-qt-client/HttpRequest.h.mustache

@@ -71,7 +71,7 @@ public:
     int  getHttpResponseCode() const;
 
 Q_SIGNALS:
-    void on_execution_finished({{prefix}}HttpRequestWorker *worker);
+    void on_execution_finished({{this}}::{{prefix}}HttpRequestWorker *worker);
     void downloadProgress(qint64 bytesReceived, qint64 bytesTotal);
 
 private: