GTK Shell: implement global menu get-set properties

[rilian-la-te]

/**
 *  In gnome-shell/mutter/meta windows/views keep track of the properties
 *  specified as arguments here.
 *  Currently only the app_id is implemented / required.
 */
static void handle_gtk_surface_set_dbus_properties(wl_client *client,
    wl_resource *resource,
    const char *application_id, const char *app_menu_path, const char *menubar_path,
    const char *window_object_path, const char *application_object_path,
    const char *unique_bus_name)
{
    auto surface = static_cast<wf_gtk_surface*>(wl_resource_get_user_data(resource));
    if (application_id)
    {
        wf::get_core().get_data_safe<wf_gtk_shell>()->surface_app_id[surface->wl_surface] = application_id;
    }
}

I think it will be good if it will be possible to query and set other properties, because it will open Global Menu to work. Maybe it is worth to make it separate plugin along with KDE global menu protocol.