Issue #1818568 by Berdir, das-peter: Convert files to the new Entity Field API.

core/includes/file.inc

...les/aggregator/lib/Drupal/aggregator/Form/OpmlFeedAdd.php

core/modules/file/file.api.php

core/modules/file/file.field.inc

core/modules/file/file.module

core/modules/file/lib/Drupal/file/FileInterface.php

core/modules/file/lib/Drupal/file/FileStorageController.php

...le/lib/Drupal/file/FileUsage/DatabaseFileUsageBackend.php

.../modules/file/lib/Drupal/file/FileUsage/FileUsageBase.php

.../modules/file/lib/Drupal/file/Plugin/Core/Entity/File.php

...upal/file/Plugin/field/formatter/GenericFileFormatter.php

...pal/file/Plugin/field/formatter/RSSEnclosureFormatter.php

.../Drupal/file/Plugin/field/formatter/UrlPlainFormatter.php

core/modules/file/lib/Drupal/file/Tests/CopyTest.php

core/modules/file/lib/Drupal/file/Tests/DeleteTest.php

core/modules/file/lib/Drupal/file/Tests/DownloadTest.php

.../modules/file/lib/Drupal/file/Tests/FileFieldPathTest.php

...es/file/lib/Drupal/file/Tests/FileFieldRSSContentTest.php

...ules/file/lib/Drupal/file/Tests/FileFieldRevisionTest.php

.../modules/file/lib/Drupal/file/Tests/FileFieldTestBase.php