Implement duplicate detection as a service

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Here's an example of the custom pre-import event that uses the service in this patch.

<?php

namespace Drupal\my_custom_migrate\EventSubscriber;

use Drupal\migrate\Event\MigrateImportEvent;
use Drupal\migrate_file_to_media\Services\DuplicateDetectionService;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Drupal\migrate\Event\MigrateEvents;

/**
 * Custom migrate event subscriber.
 */
class MyCustomMigrateSubscriber implements EventSubscriberInterface {
  /**
   * The duplicate file detection service.
   *
   * @var \Drupal\migrate_file_to_media\Services\DuplicateDetectionService
   */
  protected DuplicateDetectionService $duplicateDetectionService;

  /**
   * Constructs a MyCustomMigrateSubscriber object.
   *
   * @param \Drupal\migrate_file_to_media\Services\DuplicateDetectionService $duplicateDetectionService
   *   The search links service.
   */
  public function __construct(DuplicateDetectionService $duplicateDetectionService) {
    $this->duplicateDetectionService = $duplicateDetectionService;
  }

  /**
   * Run migrate:duplicate-file-detection before migrate_file_to_media
   * migrations.
   **
   * @param \Drupal\migrate\Event\MigrateImportEvent $event
   *   Response event.
   */
  public function onPreImport(MigrateImportEvent $event) {
    $config = $event->getMigration()->getPluginDefinition();

    if (($config['source']['plugin'] ?? '') !== 'media_entity_generator_d7') {
      return;
    }

    // Run the migrate:duplicate-file-detection command for the migration.
    $this->duplicateDetectionService->duplicateFileDetection($config['id'], [FALSE, TRUE]);
  }

  /**
   * {@inheritdoc}
   */
  public static function getSubscribedEvents() {
    return [
      MigrateEvents::PRE_IMPORT => ['onPreImport'],
    ];
  }

}

MR must be rebased from the dev branch