A11y: Closing a dropdown should return focus to the dropdown control

When a dropdown component https://getbootstrap.com/docs/5.1/components/dropdowns/ is closed, focus is currently lost (though most browsers then use heuristics to try and place it roughly in the correct area.

It should ideally be programmatically placed back to the trigger/control that opened the dropdown in the first place.

This may need an extra option to suppress this behaviour for clicks inside the dropdown, as moving focus explicitly back to the trigger/toggle may interfere with whatever the author may be doing with options/links/etc inside the dropdown