InlineEntityFormMediaWidget disregards modifications after dispatching MEDIA_ENTITY_CREATE event

Problem/Motivation

In InlineEntityFormMediaWidget::submit() we have:

  /**
   * {@inheritdoc}
   */
  public function submit(array &$element, array &$form, FormStateInterface $form_state) {
    $media_entities = $this->prepareEntitiesFromForm($form, $form_state);
    $source_field = $this->getBundle()->getTypeConfiguration()['source_field'];

    foreach ($media_entities as $media_entity) {
      $file = $media_entity->{$source_field}->entity;
      /** @var \Drupal\dropzonejs\Events\DropzoneMediaEntityCreateEvent $event */
      $event = $this->eventDispatcher->dispatch(Events::MEDIA_ENTITY_CREATE, new DropzoneMediaEntityCreateEvent($media_entity, $file, $form, $form_state, $element));
      $media_entity = $event->getMediaEntity();
      $media_entity->save();
    }

    if (!empty(array_filter($media_entities))) {
      $this->selectEntities($media_entities, $form_state);
      $this->clearFormValues($element, $form_state);
    }
  }

which is dispatching a MEDIA_ENTITY_CREATE event which allows the entity to be modified. We get the entity back from the event and save it, but we fail to keep this new value when passing the entities into the selection widget, because the for loop isn't looping by reference.

Proposed resolution

Fix this by passing to ::selectEntities() the modified entity, instead of the original one.

Remaining tasks

User interface changes

API changes

Data model changes