* Allow time fields to be omitted by constructing with `timeIncluded` as `false`.
* Ensure `reportValidity` is only called on a control when it is in an expanded section.
* Rename "ampm" to "meridian".
* Improve accessibility and fix HTML validation and style issues for both the date/time control and the preview link control.
* Fix styling of dropdowns and clean CSS.
* Improve accessibility of nav menus component.
Props westonruter, afercia, sayedwp, melchoyce.
Amends [41626].
See #39896.
Fixes#42022.
Built from https://develop.svn.wordpress.org/trunk@41670
git-svn-id: http://core.svn.wordpress.org/trunk@41504 1a063a9b-81f0-0310-95a4-ce76da25c4cd