[Translatable] Add methods to remove translations by entity, by field or by locale

[kevinkopf]

I have found myself in the situation when I needed to find and remove translations. One of the specific use cases goes like this:

1. Create a TranslationEntity

#[ORM\Table(name: 'article_translations')]
#[ORM\Index(name: 'article_translation_idx', columns: ['foreign_key', 'locale', 'object_class', 'field'])]
#[ORM\Entity(repositoryClass: TranslationRepository::class)]
class ArticleTranslation extends AbstractTranslation
{
    /**
     * All required columns are mapped through inherited superclass
     */
}

2. Set up the TranslatinoRepository (I do it in Symfony services as per docs)

# services.yaml

  Gedmo\Translatable\Entity\Repository\TranslationRepository:
    factory: [ '@doctrine.orm.entity_manager', 'getRepository' ]
    arguments:
      - 'Gedmo\Translatable\Entity\Translation'

3. Inject the repository and try to translate:

class SomeHandler
{
  public function __construct() {
    private TranslationRepository $translationRepository,
  }

  public function handle(...) {
    $this->translationRepository->translate($entity, "field", $locale, "Some value");
  }
}

When run multiple times, I end up with multiple translations in the database.

I believe, article_translation_idx should be UniqueConstraint instead of Index, but I decided to introduce the missing removal method before digging deeper into this.