MDL-78467 core_cache: Improve cache locking API

* Makes it possible to safely call acquire_lock so that it throws an
  exception instead of returning false if it can't get a lock (which
  most existing uses assumed it already does).
* Fix some omissions from the requirelockingbeforewrite option (it
  now checks on delete).
* Modinfo uses a versioned cache, so it is not necessary to delete
  items, only increase the version. (Provided we keep track of
  cacherev carefully...)

cache/classes/interfaces.php

@@ -248,8 +248,12 @@ interface cache_loader_with_locking {
      * However this doesn't guarantee consistent access. It will become the responsibility of the calling code to ensure
      * locks are acquired, checked, and released.
      *
+     * Prior to Moodle 4,3 this function used to return false if the lock cannot be obtained. It
+     * now always returns true, and throws an exception if the lock cannot be obtained.
+     *
      * @param string|int $key
-     * @return bool True if the lock could be acquired, false otherwise.
+     * @return bool Always returns true (for backwards compatibility)
+     * @throws moodle_exception If the lock cannot be obtained after a timeout
      */
     public function acquire_lock($key);