- adds a "search" icon into the search fields
- adds a hidden description for the widget search field, targeted by `aria-describedby`
- adds the "clear-results" button to the widgets search
- removes the `change` and `search` events bound on the widget search, for these "live searches" WordPress should standardize on `input` (+ `keyup` when needed)
- adds property and function to keep track and update the number of the widgets search results
- the widgets search results are now announced via `wp.a11y.speak()`
- adds a visible and audible message when there are no widgets search results
- moves some CSS to `customize-controls.css`
Props ryankienstra, melchoyce, afercia.
Fixes#36908.
Built from https://develop.svn.wordpress.org/trunk@38709
git-svn-id: http://core.svn.wordpress.org/trunk@38652 1a063a9b-81f0-0310-95a4-ce76da25c4cd
