D7FieldCollectionItemDeriver constructor.
string $base_plugin_id: The base plugin ID for the plugin ID.
\Drupal\migrate_drupal\FieldDiscoveryInterface $field_discovery: The migration field discovery service.
public function __construct($base_plugin_id, FieldDiscoveryInterface $field_discovery) {
$this->basePluginId = $base_plugin_id;
$this->fieldDiscovery = $field_discovery;
}