Update display.js to include display:contents utility class

[mtimbs]

Add utility class for display: contents. This is useful for flex and grid. You can read more here https://css-tricks.com/get-ready-for-display-contents/

[adamwathan]

Thanks!

[knowler]

One should use display: contents very cautiously as there is an accessibility impact involved with its effect despite its apparent usefulness for other applications. I'd go as far as not including it as an out-of-the-box Tailwind utility and leave it up to userland to add via config or plugin if needed. It is just one rule, but given Tailwind's pervasiveness and the general lack of accessibility knowledge amongst developers (especially in regards to strange cases like this), this one would be best left out of immediate reach (for now).