For all CSS generated icons across core, either add `aria-hidden="true"` to the HTML wrapper or set the generated content alternative to an empty string in the CSS using the alternative text specification for CSS generated content.
Props afercia, joedolson, cheffheid, jhabdas.
Fixes#40428.
Built from https://develop.svn.wordpress.org/trunk@60806
git-svn-id: http://core.svn.wordpress.org/trunk@60142 1a063a9b-81f0-0310-95a4-ce76da25c4cd
69bb40f683