The WCAG 2.2 AA rules of axe-core are never run in the accessibility validation

Problem

The axe-core validation of the Docker functional tests only selects rules by the tags wcag2a, wcag2aa, wcag21a and wcag21aa. The wcag22aa tag is missing, so target-size, the only WCAG 2.2 AA rule of axe-core, is never executed. This happens even though WCAGContext configures it to fail the build. Our official accessibility commitment is WCAG 2.2 AA.

The same tag list is duplicated in assert-axe.ts of @xwiki/platform-test-accessibility, which the Vitest accessibility tests use.

Proposal

• Add wcag22aa to VALIDATE_TAGS in WCAGContext and to the tag list of assert-axe.ts.
• Fix or report the target-size violations it reveals, and keep the rule warning-only until they are fixed.

Raised in https://forum.xwiki.org/t/remove-the-dutch-web-guidelines-validation/19056