* update playground examples to use a shared `Button`
* expose a `ui-focus-visible` variant
* keep track of a `data-headlessui-focus-visible` attribute
* do not set the `tabindex`
The focus was always set, but the ring wasn't showing up. This was also
focusing a ring when the browser decided not the add one.
Let's make the browser decide when to show this or not.
* update changelog
Robin Malfait