Fix "The "file_download_link" plugin does not exist." error. the media_extra module to be installed.

fix-upgrade_d7_field_formatter_settings-migration.patch

diff --git a/core/modules/file/src/Plugin/migrate/field/d6/FileField.php b/core/modules/file/src/Plugin/migrate/field/d6/FileField.php
index 804e34a655..0d4b4d3f64 100644
--- a/core/modules/file/src/Plugin/migrate/field/d6/FileField.php
+++ b/core/modules/file/src/Plugin/migrate/field/d6/FileField.php
@@ -38,6 +38,7 @@ public function getFieldFormatterMap() {
       'image_plain' => 'image',
       'image_nodelink' => 'image',
       'image_imagelink' => 'image',
+      'file_download_link' => 'generic_media_link',
     ];
   }