fix: deprecated creation of dynamic property

@see https://php.watch/versions/8.2/dynamic-properties-deprecated

Author: slevesque

jsonld.php

@@ -5979,6 +5979,10 @@ public function next() {
  * the overhead of recomputing them.
  */
 class ActiveContextCache {
+  protected $order = [];
+  protected $cache;
+  protected $size;
+
   /**
    * Constructs a new ActiveContextCache.
    *