Add Media Panel: Announce context of close button for screen readers

[joedolson]

The current text of the Add Media Panel close button is just "Close". For screen readers, it's important to be notified what will be closed when you select this option, so that they can be certain that they're closing the right thing.

Changes text to "Close Media Panel" to provide context for screen readers.

Same patch also changes Close text from being a title attribute (which will only be announced in some screen readers with some configurations) screen-reader-hidden text.

Related: #25105

[joedolson]

Provide context for close; move to screen reader text

[afercia]

hi,
if just text, esc_attr_e should be removed in favor of just _e
I would suggest also to don't use capitalized first letters for "Close Media Panel". These things tend to be confusing for translators and often lead to have duplicated strings to translate, the capitalized version, the non-capitalized version...

[joedolson]

Updates per suggestions from afercia

[michalzuber]

How about "Close media modal dialog" ?

[wonderboymusic]

In 29295:

Media Grid: change text to "Close Media Panel" to provide context for screen readers.

Props joedolson.
Fixes #28976.