Image: Fix inclusion of alttext in lightbox button aria-label

[artemiomorales]

What?

The logic to include alttext in the lightbox button's aria-label was not working properly, and screen readers were not able process that information as a result. This fixes that.

Why?

We want users who use screen readers to have a good experience when navigating pages that contain the lightbox.

How?

It adds back a line of logic that had been accidentally removed that allows us to create the aria-label with the alttext.

Testing Instructions

1. Add an image to a post
2. Add alt text to the image
3. In the image block's settings, make sure "Expand on Click" is enabled
4. Publish and view the post using a screen reader
5. Tab to the image and make sure the alt text is announced by the screen reader

Testing Instructions for Keyboard

N/A (specified above)

[afercia]

Thanks for working on this.
Noting that I previously created #54971 and was working on this fix and more fixes. Pull requeste without related issues are somewhat difficult to find for other contributors in a large open source project. A little more coordination would be apprciated.

That said, I think the same fix should be applied also to the file in the block-supports?

[afercia]

At line 138 the $processor instance is used again but now it points to the img. To my understanding, a new instance should be created before using get_updated_html()?

[artemiomorales]

@afercia Perfect, thanks for taking a look at this and capturing the other issues in #54971 🙏

Since it looks like you've already begun addressing this issue in depth in #55010, I'll go ahead and close this PR, though I can open it back up and continue working on it if that makes sense.

[artemiomorales]

Pull requeste without related issues are somewhat difficult to find for other contributors in a large open source project. A little more coordination would be apprciated.

@afercia Pardon, got it, will be sure to create related issues for PRs going forward to make sure we coordinate more effectively 👍