[Policy] Officially move to WCAG 2.2 AA Support

Suggestion for remaining tasks: Configure our Nightwatch implementation to use 2.2 for all Axe tests.

From an Olivero and CSS maintainer position, a big +1.

It's something that I don't believe will create a ton of issues. If issues are identified, they should be fixed. Plus, it makes Drupal's accessibility look behind the times if we say we only officially support 2.1.

Adding some related issues.

I think my main question is if an issue brings a UI up to 2.1 (or keeps it at 2.1), but a 2.2 issue is discovered with that same UI, then I don't think we should block on 2.2 issues but open separate issues to deal with those. I don't know if that's even a real concern though.

If/when we do 📌 Automated A11y tests in PHPUnit Active I would also want the option to set it to a lower level if we can get tests to pass, then open another issue to go to 2.2 and open issues to fix those issues so we can enforce it. We've done this for many similar changes like phpstan because the tests prevent the regressions even at a lower level, whereas no tests don't prevent any regressions at all.

Both of these are about how we get towards 2.2 rather than whether we should though, it makes sense to have that as the target.

@catch:

I would also want the option to set it to a lower level if we can get tests to pass.

The current MR on 📌 Automated A11y tests in PHPUnit Active supports passing Axe options with individual tests. The options can include the WCAG versions / levels to run (as tags). The test for that can be improved to explicitly test for disabling WCAG 2.2. Would that do it?