[Cache] Added reserved characters constant for CacheItem

Author: andyexeter

ItemInterface.php

@@ -37,6 +37,11 @@ interface ItemInterface extends CacheItemInterface
      */
     const METADATA_TAGS = 'tags';
 
+    /**
+     * Reserved characters that cannot be used in a key or tag.
+     */
+    const RESERVED_CHARACTERS = '{}()/\@:';
+
     /**
      * Adds a tag to a cache item.
      *