[Task Manager] React to activities changes

A window can be moved to another activity externally, for example using
the user actions menu in kwin. The window model should notify the task
manager when such an event occurs.

libtaskmanager/waylandtasksmodel.cpp

@@ -314,6 +314,14 @@ void WaylandTasksModel::Private::addWindow(KWayland::Client::PlasmaWindow *windo
     QObject::connect(window, &KWayland::Client::PlasmaWindow::applicationMenuChanged, q, [window, this] {
         this->dataChanged(window, QVector<int>{ApplicationMenuServiceName, ApplicationMenuObjectPath});
     });
+
+    QObject::connect(window, &KWayland::Client::PlasmaWindow::plasmaActivityEntered, q, [window, this] {
+        this->dataChanged(window, Activities);
+    });
+
+    QObject::connect(window, &KWayland::Client::PlasmaWindow::plasmaActivityLeft, q, [window, this] {
+        this->dataChanged(window, Activities);
+    });
 }
 
 AppData WaylandTasksModel::Private::appData(KWayland::Client::PlasmaWindow *window)