Deprecated code in src/Form/ExtraFieldAddForm.php

@liliet best practice is to have your trait definitions be listed immediately following the class definition:

class ExtraFieldAddForm extends FormBase {

  use MessengerTrait;

  protected $currentStep;


  public function __construct(MessengerInterface $messenger) {
    ...
  }

  ...

}

I'm moving this to need work, other than that once it's fixed this should be good to go for RTBC. Thank you! :)