Privacy: add means to export personal data by username or email address. Generate a zipped export file containing all data. First run.

Props allendav.
See #43546.

git-svn-id: https://develop.svn.wordpress.org/trunk@43012 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/user.php

@@ -3145,7 +3145,7 @@ function wp_validate_user_request_key( $request_id, $key ) {
  * @since 4.9.6
  *
  * @param int $request_id Request ID to get data about.
- * @return array|false
+ * @return WP_User_Request|false
  */
 function wp_get_user_request_data( $request_id ) {
 	$request_id = absint( $request_id );