Added functions to retrieve associated parts of an element within twig labels

This fixes #1239

src/Services/LabelSystem/SandboxedTwigFactory.php

@@ -114,6 +114,7 @@ final class SandboxedTwigFactory
         'barcode_svg',
         //SandboxedLabelExtension
         'placeholder',
+        'associated_parts', 'associated_parts_count', 'associated_parts_r', 'associated_parts_count_r',
         ];
 
     private const ALLOWED_METHODS = [