When some screen option input fields are changed (post table columns, welcome panel, and metabox visibility), the change is saved to options. Other screen options (e.g. number of items per page) are only saved on submit. The changes that are saved immediately are visibly changed for sighted readers immediately. Change adds a `wp.a11y.speak()` call to inform screen readers that a value change has updated screen options.
Props kkmuffme, joedolson, yogeshbhutkar, audrasjb, sourabhjain.
Fixes#62550.
Built from https://develop.svn.wordpress.org/trunk@59988
git-svn-id: http://core.svn.wordpress.org/trunk@59330 1a063a9b-81f0-0310-95a4-ce76da25c4cd
5c784a1001