radix_form_element doesn't handle #title_display "after" correctly

When using a "select" form element that has the #title_display set to "after", the actual select dropdown is not displayed. This can be reproduced in Open Atrium by creating an Event and checking the "Repeats" option, then selecting "Monthly" and notice that the day of the week field to repeat is not rendered. (See #2535948: Errors when planning repeatable events on Nth day of month).

When comparing the radix_form_element() function with the default Drupal theme_form_element(), you can see the code that is missing and needs to change. Radix handles the special case of radio/checkboxes that need to go inside the label, but in the else condition doesn't render the children for other field types.

Patch coming next.