Deprecate 46ca7f (Element marked as decorative is not exposed)

[tombrunet]

We started looking into this due to Fail 2 on 46ca7f (See related issue in the other repo: w3c/wcag-act-rules#295)

Fail 2 from https://www.w3.org/WAI/standards-guidelines/act/rules/46ca7f/ is no longer supported by any standards after changes in https://www.w3.org/TR/html-aria/ clarified the img to role mappings to be based on whether or not it has an accessible name rather than based on alt attribute.

The decorative concepts that are the foundation of 46ca7f are no longer supported due to spec changes. Additionally, the browsers seem to all handle conflict resolution correctly now, seeming to invalidate the accessibility supports notes.

There is a PR that should introduce a rule that should be more accurate: #2195

[dan-tripp-siteimprove]

We (Giacomo, Carlos, and I) discussed this in the office hours today. We think that there are really two intentions behind this rule: 1) conflict resolution and 2) "mismatching intentions". We got the wording of (2) from the background of the rule. (1) is (or will be) handled better by #2195 but (2) is not.

The rule is not mapping to WCAG so tool vendors have leeway in whether and how to flag this to their users (violations, warning, or nothing).