Accessibility improvements - Progress dropdown menu

[robinmolen]

This ticket describes accessibility improvements for the progress menu, when it's used as a dropdown (when viewed on small screens or greatly zoomed-in).

• 4.1.2 (name, role, value) The dropdown variant of the progress menu doesn't contain aria-expanded information
• 2.4.7 (navigation - focus visibility) When the form is displayed on a small screen, or greatly zoomed-in, the progress menu will be shown as a dropdown menu. When you focus any menu items in the dropdown, and repeatable press the tab key, you can place the focus outside the menu. The menu stays expended, resulting in the focused element not being visible.