cards: improve a11y alt text in generated img tag

[jcharousset]

Hello,

Thank you for all the work you’ve put into this project — it’s impressive and very helpful.

The new "cards" shortcode is nice, and the "children" shortcode with "type=cards" even more. However the generated tag doesn't have an alt text, which is flagged as an error by many HTML proofers.

A quick & easy solution could be to always add an empty alt text in the generated tag. This sort of makes senses to me, as images in cards are frequently associated with a title and/or description, so they could be considered decorative. Maybe in the future this could be extended with a mechanism allowing to specify an alt text.

[McShelby]

Hey @jcharousset, thanks for the praise and your input.

I don't want sound too harsh, but I will not start littering empty attributes around just to fulfill validators needs while the semantic is still broken.

I more tend to role="presentation" for the images but that should only happen if we also show the title. With image-only cards, the title should be in the alt attribute. So it's a bit more work to do it right.