Consider iterating text on media upload for alt text

[karmatosed]

This could be confusing both in what it does and linking to an external source. It might be a good idea to work on some ideas to improve the copy here and also linking.

[melchoyce]

Historical context in #41612

[hellofromTonya]

#51616 was marked as a duplicate.

[hellofromTonya]

Merging @garrett-eclipse description from a duplicate ticket #51616:

On Media Modals the Alt Text has a description containing a link 'Describe the purpose of the image.' that's a little misleading to new users. It feels less a description and information and more an action in that users click it thinking that's how one would describe the image but instead find it's just information.

Could a little (i) icon be added to denote it as informational. Or could we adjust the language;
_Alt Text_ describes the image purpose.
*Where just the 'Alt Text' part is links.
This i feel would take the link off the action word which is what currently makes the link feel like an action and not just extra information.

Love the concept of the feature just think we can remove the ambiguity of the link purpose.

[afercia]

Linking to the related issue and PR on the Gutenberg repo:
​https://github.com/WordPress/gutenberg/issues/19068
​https://github.com/WordPress/gutenberg/pull/26520

The key concepts the accessibility team want to communicate with this text and that were discussed on #41612 and related conversations on Slack are the the following 3 ones:

• The alt text describes the purpose of the image, it's not the image description. The image purpose can be very different from the image content depending on usage and context.
• The link points to a resource that explains this concept in detail: the W3C "alt decision tree"
• In most of the cases, images are purely decorative and don't need an alt text. The part "Leave empty if the image is purely decorative" is fundamental to communicate this concept to users as they tend to think they have to provide an alt text in all cases (which is wrong)

Improvements to the current text are welcome as long as these three points are cleaerly communicated. Proposal with minimal change:

[link]Learn how to describe the purpose of the imagelink. Leave empty if the image is purely decorative.