File component configuration does not have theming in Form Builder

Right now in Form Builder, all File components just show a long list of checkboxes for extensions when configuring the Validation options. With recent changes over in #1467182: Update the file component configuration theming and JavaScript, we can easily update the Form Builder integration so that these options display properly. Patch attached. I'm not sure if we should leave the existing code in place or not, but keeping it there gives us backwards compatibility for a transition. Patch applies to both D6 and D7.