Accessibility: Media: Improve accessibility of the status and error messages in the Image Editor.

- improves focus management by moving focus to the notices, if any, or to the first "tabbable" element
- this avoids a focus loss and helps Braille-only and screen magnification users to be aware of the messages
- adds an ARIA role `alert` to all the notices 
- uses `wp.a11y.speak()` to announce messages to assistive technology
- this way, all visual users will see the messages while assistive technology users will get an audible message
- uses `wp.i18n` for translatable strings in `wp-admin/js/image-edit.js`

Props anevins, ryanshoover, antpb, SergeyBiryukov, afercia.
See #20491.
Fixes #47147.


git-svn-id: https://develop.svn.wordpress.org/trunk@48375 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/css/media-views.css

@@ -1998,7 +1998,8 @@
 	display: block;
 }
 
-.media-modal .imgedit-wrap div.updated {
+.media-modal .imgedit-wrap div.updated, /* Back-compat for pre-5.5 */
+.media-modal .imgedit-wrap .notice {
 	margin: 0;
 	margin-bottom: 16px;
 }