Improve targeting for the `sortableItems`, resolving an issue where the first `<li>` in the control became a sortable target, allowing the user to drag a single top level menu outside the intended sortable area.
props adamsilverstein.
fixes#32738.
#wceu
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* Add a description and an `aria-describedby` attribute to inform users this is a "live" search.
* Announce the number of search results via `wp.a11y.speak`.
* Use `aria-busy` attribute to stop screen readers announcing content while the "loading more results" is running.
* Increase the search debounce wait interval to 500ms to be consistent with other live searches.
* If a search fails don't call `wp.a11y.speak` with an undefined variable.
props afercia.
see #32720.
Built from https://develop.svn.wordpress.org/trunk@32891
git-svn-id: http://core.svn.wordpress.org/trunk@32862 1a063a9b-81f0-0310-95a4-ce76da25c4cd
