Accessibility: Improve the Tags meta box accessibility.

- changes the "X" links in buttons, improves their color contrast ratio and focus style
- adds screen reader text "Remove item: + tagname"
- uses `wp.a11y.speak()` to give screen reader users feedback when adding/removing tags
- makes the `tagcloud-link` toggle a button, with an `aria-expanded` attribute to indicate the tag cloud collapsed/expanded state
- changes colors for the autocomplete highlighted option in order to have a better color contrast ratio
- reduces the font size for the autocomplete on Press This
- removes CSS related to the old `suggest.js` from Press This

Props joedolson, cgrymala, azaozz, afercia.
Fixes #27555.

Built from https://develop.svn.wordpress.org/trunk@38880


git-svn-id: http://core.svn.wordpress.org/trunk@38823 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/script-loader.php

@@ -538,6 +538,10 @@ function wp_default_scripts( &$scripts ) {
 		$scripts->add( 'tags-suggest', "/wp-admin/js/tags-suggest$suffix.js", array( 'jquery-ui-autocomplete', 'wp-a11y' ), false, 1 );
 		did_action( 'init' ) && $scripts->localize( 'tags-suggest', 'tagsSuggestL10n', array(
 			'tagDelimiter' => _x( ',', 'tag delimiter' ),
+			'removeTerm'   => __( 'Remove term:' ),
+			'termSelected' => __( 'Term selected.' ),
+			'termAdded'    => __( 'Term added.' ),
+			'termRemoved'  => __( 'Term removed.' ),
 		) );
 
 		$scripts->add( 'post', "/wp-admin/js/post$suffix.js", array( 'suggest', 'wp-lists', 'postbox', 'tags-box', 'underscore', 'word-count', 'wp-a11y' ), false, 1 );