Error to select widget flexbox in field image

Image fields have an extra wrapper added via ajax that prevents our classes from working correctly to get the styles. I don't unfortunately have a solution that gets around this and honestly think the inconsistencies in Drupal form widget wrappers due to use of ajax is a problematic issue to improve upon with theming.

Here's a patch that adds an after_build function to add class to the ajax wrapper for managed_file types (ie; file/image form elements). Please test this with flexbox classes set for these form element types and ensure the class is applied to the most outer div and that files/images still upload normally. My own testing locally shows this issue resolved with this patch.