Menu Button & Listbox Button: overlay does not collapse when focus returns to button

[ianmcburnie]

Currently when we shift tab from the listbox or menu item back to the button, the overlay stays open. I believe this was by design originally, but in retrospect I think it would probably make more sense if the overlay collapses (and can then easily be opened by SPACEBAR/ENTER again). Let's investigate.

[saiponnada]

Currently the menu button in APG, auto closes when we shift the focus back. I do not see any reason not to do this with listbox-button as well.

https://www.w3.org/WAI/ARIA/apg/patterns/menu-button/examples/menu-button-actions-active-descendant/

How about exposing a configurable option (by default set to true) something like this - autoCollapse: true? or is autoCollapse too generic?

[ianmcburnie]

I think we use 'autoCollapse' in a few other places, typically for when the focus leaves the entire widget. But here, the button is technically still part of the widget.

We might not need to add a configuration option at all. If we feel that menu-button and listbox-button should always collapse when focus moves back to button let's just make that the behavior.

[saiponnada]

Fixed this issue in #205