Issue #3416306 by rodrigoaguilera: Add support for exposing files in media fields

src/Plugin/Field/FieldFormatter/InformeaMediaFilesFormatter.php

+<?php
+
+namespace Drupal\informea_api\Plugin\Field\FieldFormatter;
+
+use Drupal\Core\Field\EntityReferenceFieldItemListInterface;
+use Drupal\Core\Field\FieldItemListInterface;
+use Drupal\media\MediaInterface;
+
+/**
+ * Plugin implementation of the 'informea_api_media_files' formatter.
+ *
+ * Use this plugin instead of informea_api_files when the documents
+ * that want to be exposed are media references.
+ *
+ * @FieldFormatter(
+ *   id = "informea_api_media_files",
+ *   label = @Translation("[InforMEA] Media Files"),
+ *   field_types = {
+ *     "entity_reference",
+ *   }
+ * )
+ */
+class InformeaMediaFilesFormatter extends InformeaFilesFormatter {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function viewElements(FieldItemListInterface $items, $langcode) : array {
+    if (!$items instanceof EntityReferenceFieldItemListInterface) {
+      return [];
+    }
+    $files = [];
+    foreach ($items->referencedEntities() as $media) {
+      if (!$media instanceof MediaInterface) {
+        continue;
+      }
+      /** @var \Drupal\media\Plugin\media\Source\File $source */
+      $source = $media->getSource();
+      $configuration = $source->getConfiguration();
+      $files = array_merge($files, $this->getFiles($media->get($configuration['source_field'])));
+    }
+    return $this->serialize($files);
+  }
+
+}