Addition: allow aria-hidden on picture element

[scottaohara]

Revise the allowances for the picture element to allow for the aria-hidden attribute.

Need at least two checkers to accept this change before we can merge.

Closes #346

• [x] html validator
• [x] ibm equal access accessibility checker
• [x] axe-core (already allows this)
• [x] arc toolkit

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Preview | Diff

[scottaohara]

nit: need to update this PR to link aria-hidden ref to the aria spec. Github is being wonky right now, so adding this as a reminder.

[marcoscaceres]

Note, you need to do the same for the other pull requests.

I'll review those and make sure it's all good. Feel free to also ping me for review on those.

However, we don't need to wait to merge things into the Editor's draft.

The minute the spec gets published as REC, we can then start pushing all the ".addition" to /TR/.

In the meantime, I've disabled the auto-publish.yml script.

[marcoscaceres]

Actually, it's a little more nuanced:

https://github.com/w3c/tr-design/blob/e40643f08e80f65a31d54ab2fb9e3ca34fa6cfcc/src/base.css#L35-L38

 *   - .correction for "candidate corrections"       (div, aside, details, section)
 *   - .addition   for "candidate additions"         (div, aside, details, section)
 *   - .correction.proposed for "proposed corrections" (div, aside, details, section)
 *   - .addition.proposed   for "proposed additions"   (div, aside, details, section)

The things in the process are outlined in: https://www.w3.org/Consortium/Process/Drafts/#revising-rec