Enable display configuration for transform when it's enabled for view

Closes #3413107

transform_api.module

@@ -82,3 +82,17 @@ function transform_api_entity_transform_mode_presave(EntityTransformModeInterfac
 function transform_api_entity_transform_mode_delete(EntityTransformModeInterface $transform_mode) {
   \Drupal::service('router.builder')->setRebuildNeeded();
 }
+
+/**
+ * Implements hook_entity_base_field_info_alter().
+ */
+function transform_api_entity_base_field_info_alter(&$fields, \Drupal\Core\Entity\EntityTypeInterface $entity_type) {
+  /** @var \Drupal\Core\Field\BaseFieldDefinition $field */
+  foreach ($fields as $field) {
+    // If the field is configurable for view display
+    // then it should be configurable for a transform mode.
+    if ($field->isDisplayConfigurable('view')) {
+      $field->setDisplayConfigurable('transform', TRUE);
+    }
+  }
+}