MDL-67594 core_lock: Deprecate extend()

cache/upgrade.txt

@@ -5,6 +5,7 @@ Information provided here is intended especially for developers.
 * The function supports_recursion() from the lock_factory interface has been deprecated including the related implementations.
 * The function extend_lock() from the lock_factory interface has been deprecated without replacement including the related
   implementations.
+* The function extend() from the lock class has been deprecated without replacement.
 
 === 3.9 ===
 * The record_cache_hit/miss/set methods now take a cache_store instead of a cache_definition object

lib/classes/lock/lock.php

@@ -80,10 +80,15 @@ public function get_key() {
 
     /**
      * Extend the lifetime of this lock. Not supported by all factories.
+     *
+     * @deprecated since Moodle 4.0.
      * @param int $maxlifetime - the new lifetime for the lock (in seconds).
      * @return bool
      */
     public function extend($maxlifetime = 86400) {
+        debugging('The function extend() is deprecated, please do not use it anymore.',
+            DEBUG_DEVELOPER);
+
         if ($this->factory) {
             return $this->factory->extend_lock($this, $maxlifetime);
         }