Extend ImportSource interface to list files of a folder

Signed-off-by: Christopher Ng <chrng8@gmail.com>

Author: Pytal

lib/public/UserMigration/IImportSource.php

@@ -53,6 +53,16 @@ public function getFileContents(string $path): string;
 	 */
 	public function getFileAsStream(string $path);
 
+	/**
+	 * List the files of a folder
+	 *
+	 * @param string $path Full path to the folder in the export archive.
+	 * @return array The list of files.
+	 *
+	 * @since 24.0.0
+	 */
+	public function getFolderListing(string $path): array;
+
 	/**
 	 * Copy files from the export to a Folder
 	 *