MDL-77350 cache: Added class properties that are not declared

In PHP 8.2 and later, setting a value to an undeclared class property is
deprecated and emits a deprecation notice.
So we need to add missing class properties that still need to be declared.

cache/classes/loaders.php

@@ -173,6 +173,19 @@ class cache implements cache_loader {
      */
     protected $subloader = false;
 
+    /**
+     * Gets set to true if the cache writes (set|delete) must have a manual lock created first.
+     * @var bool
+     */
+    protected $requirelockingbeforewrite = false;
+
+    /**
+     * Gets set to true if the cache's primary store natively supports locking.
+     * If it does then we use that, otherwise we need to instantiate a second store to use for locking.
+     * @var cache_store|null
+     */
+    protected $nativelocking = null;
+
     /**
      * Creates a new cache instance for a pre-defined definition.
      *