Add banner on the themes archive when a search is done for accessibility ready to add context on what this designation means

[alh0319]

Currently, when a user searches the theme directory for Accessibility Ready themes, there is no indication of what this tag means. Some users may misconstrue this tag as meaning that the theme is fully WCAG compliant.

We would like to add an alert to the top of the theme search that explains what the tag means if a user chooses to filter by it. As more laws around the world require websites to conform to WCAG, this distinction is increasingly important.

Proposed text:

Themes labeled as accessibility-ready have been independently reviewed against a set of WordPress-specific [theme accessibility requirements]​https://make.wordpress.org/themes/handbook/review/accessibility/required/. They have not been tested for [Web Content Accessibility Guidelines]​https://www.w3.org/TR/WCAG22/ conformance.
There should be a reference to relevant WCAG criteria under each section.

Location

This banner would be visible on ​https://wordpress.org/themes/tags/accessibility-ready/ or any search that included the accessibility ready tag, such as ​https://wordpress.org/themes/tags/accessibility-ready+block-patterns+custom-background/

Design
@slferguson has a proposed design to upload.

[ndiego]

@ryelle @fcoveram @markoserb @joen, what do you all think about this approach to providing more clarity about the category? I could see something similar done for other categories as well. This is the search archive version of #7714 for the "Accessibility ready" category.

[Joen]

I shared an alternate mockup that's based on your lovely work here, but without the boxed banner treatment, in the other issue, here: https://meta.trac.wordpress.org/ticket/7714#comment:3

[fcoveram]

I like @Joen's versions shared in https://meta.trac.wordpress.org/ticket/7714#comment:3