Proxies to the plugin class' form method.
@todo This needs more explanation, an documentation. Also "proxies" is a weird word to use.
or two, and parameter
function system_plugin_ui_form($form, &$form_state, $plugin, $facet = NULL) {
$plugin_ui = drupal_container()
->get('plugin.manager.system.plugin_ui')
->createInstance($plugin);
$form = $plugin_ui
->form($form, $form_state, $facet);
$form['#validate'][] = array(
$plugin_ui,
'formValidate',
);
$form['#submit'][] = array(
$plugin_ui,
'formSubmit',
);
return $form;
}