[VarDumper] Add Caster::PATTERN_PRIVATE to help builing key

Author: lyrixx

Caster/Caster.php

@@ -36,6 +36,8 @@ class Caster
     public const PREFIX_VIRTUAL = "\0~\0";
     public const PREFIX_DYNAMIC = "\0+\0";
     public const PREFIX_PROTECTED = "\0*\0";
+    // usage: sprintf(Caster::PATTERN_PRIVATE, $class, $property)
+    public const PATTERN_PRIVATE = "\0%s\0%s";
 
     /**
      * Casts objects to arrays and adds the dynamic property prefix.