Returns a form to configure settings for the formatter.
Invoked from \Drupal\field_ui\Form\FieldInstanceEditForm to allow administrators to configure the formatter. The field_ui module takes care of handling submitted form values.
array $form: The form where the settings form is being included in.
array $form_state: An associative array containing the current state of the form.
array The form elements for the formatter settings.
Overrides FormatterInterface::settingsForm
public function settingsForm(array $form, array &$form_state) {
return array();
}