Media Library 'featured image' dialogue missing link text that describes 'opens in new tab'.

[anthonyburchell]

Describe the bug
This was originally reported in https://core.trac.wordpress.org/ticket/48028

This github issue is being created because the bug was introduced via Gutenberg and will need to happen here to resolve the overall Accessibility bug.

Description from Trac Report:

The "Media Library" panel of the "Featured Image" modal dialog contains a link labelled with "Edit image". This link takes users to a new window/tab, but that link does not inform users that it opens a new window or tab.
A link does not naturally convey itself to assistive technology that it opens in a new tab without link text that describes it.
It is important to convey that a link opens in a new tab because of the change of context may not be clear to everyone.
Suggested solution
Write more descriptive link text that describes the link opening in a new tab;
Utilise the class of 'screen-reader-text' in CSS to hide that text (you can wrap the text in ).
Example of solution

Edit Image
(Opens in a new window)

This problem was originally raised on ticket #47137 and has been separated out here to reduce complexity.

To reproduce
Steps to reproduce the behavior:

1. Add an image block
2. Click on 'media library'
3. Select image
4. Click "Edit Image" in the sidebar
   After 4 you will see this opens in a new tab. This is due to the fact that the required edit state logic is not currently in the MediaUpload component.

Expected behavior
Instead of opening in a new tab, the link should just open the Edit Image state within the same modal.

Screenshots

[anthonyburchell]

PR to resolve this is here: #17641

[anthonyburchell]

Additionally, the PR above addresses another issue that needed to be fixed in order for the edit image fix to work. Currently we use return wp.media.view.MediaFrame.Post.extend( { for the gallery views of the media library. We should instead be using return wp.media.view.MediaFrame.Select.extend( {