Add a signature to the query, if such a thing is feasible.
This signature is something that can be used when perusing query logs to discern where particular queries might be coming from.
view $view: The view which is executed.
Overrides QueryPluginBase::add_signature
function add_signature(ViewExecutable $view) {
$view->query
->add_field(NULL, "'" . $view->storage
->get('name') . ':' . $view->current_display . "'", 'view_name');
}