fix deprecations: use choices_as_values=true and flip content of the choice options

Controller/CustomFieldsGroupController.php

@@ -254,7 +254,8 @@ class CustomFieldsGroupController extends Controller
                     'csrf_protection' => false
                     ))
               ->add('type', ChoiceType::class, array(
-                    'choices' => $fieldChoices
+                    'choices' => array_combine(array_values($fieldChoices),array_keys($fieldChoices)),
+                    'choices_as_values' => true
                    ))
               ->add('customFieldsGroup', HiddenType::class)
               ->add('submit', SubmitType::class);