Add [open] variant

[reinink]

This PR adds a new [open] attribute selector variant to Tailwind CSS. This is based on the work started by @seanpdoyle in #4627. This can be useful for applying styles to <details> or <dialog> elements based on whether they are open.

<details class="border-0 open:border-1" open>
  <!-- ... -->
</details>

<details class="border-0 open:border-1">
  <!-- ... -->
</details>

This can also be combined with group and peer variants:

<details class="group peer" open>
  <summary>
    <span class="hidden group-open:inline">Close me, I'm open</span>
    <span class="inline group-open:hidden">Open me, I'm closed</span>
  </summary>
</details>

<span class="hidden peer-open:inline">I'm next to an open element</span>
<span class="inline peer-open:hidden">I'm next to a closed element</span>