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.


git-svn-id: https://develop.svn.wordpress.org/trunk@38880 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/meta-boxes.php

@@ -442,7 +442,7 @@ function post_tags_meta_box( $post, $box ) {
 	<div class="tagchecklist"></div>
 </div>
 <?php if ( $user_can_assign_terms ) : ?>
-<p class="hide-if-no-js"><a href="#titlediv" class="tagcloud-link" id="link-<?php echo $tax_name; ?>"><?php echo $taxonomy->labels->choose_from_most_used; ?></a></p>
+<p class="hide-if-no-js"><button type="button" class="button-link tagcloud-link" id="link-<?php echo $tax_name; ?>" aria-expanded="false"><?php echo $taxonomy->labels->choose_from_most_used; ?></button></p>
 <?php endif; ?>
 <?php
 }