MDL-81919 core: Update moved file namespaces

lib/classes/exception/file_serving_exception.php

@@ -14,12 +14,13 @@
 // You should have received a copy of the GNU General Public License
 // along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
 
+namespace core\exception;
 
 /**
  * An exception that indicates that file can not be served
  *
  * @package    core
- * @subpackage lib
+ * @subpackage exception
  * @copyright  2010 Petr Skoda {@link http://skodak.org}
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
@@ -33,3 +34,8 @@ class file_serving_exception extends moodle_exception {
         parent::__construct('cannotservefile', 'error', '', null, $debuginfo);
     }
 }
+
+// Alias this class to the old name.
+// This file will be autoloaded by the legacyclasses autoload system.
+// In future all uses of this class will be corrected and the legacy references will be removed.
+class_alias(file_serving_exception::class, \file_serving_exception::class);