For a number of years, the Media modal missed an explicit ARIA role and the required attributes for modal dialogs.
This was confusing for assistive technology users, since they may not realize they're inside a dialog, and that consequently the keyboard interactions may be different from the rest of the page. Lack of an explicit label for the dialog was confusing as well, since assistive technology users didn't have an immediate sense of what the dialog is for.
This change makes the Media modal meet the ARIA Authoring Practices recommendations, helping users better understand the purpose and interactions with the modal. Also, it makes sure to hide the rest of the page content from assistive technologies, until support for `aria-modal="true"` improves.
Additionally:
- moves the modal H1 heading to the beginning of the modal content
- changes the modal left menu position to make visual and DOM order match
- improves the `wp.media.view.FocusManager` documentation
Fixes#47145.
Built from https://develop.svn.wordpress.org/trunk@45572
git-svn-id: http://core.svn.wordpress.org/trunk@45383 1a063a9b-81f0-0310-95a4-ce76da25c4cd
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