Add a11y guidance for user agents

[MasterKale]

trafficstars

This PR adds informative guidance to user agents encouraging them to mediate presentation and issuance requests in a way that supports a wide range of accessible inputs and outputs.

The intent is to submit this content in the horizontal review request to the a11y-request repo.

Partially closes #229

The following tasks have been completed:

• [ ] Modified Web platform tests (link)

Implementation commitment:

• [ ] WebKit (link to issue)
• [ ] Chromium (link to issue)
• [ ] Gecko (link to issue)

Documentation and checks

• [ ] Affects privacy
• [ ] Affects security
• [ ] Pinged MDN
• [ ] Updated Explainer
• [ ] Updated digitalcredentials.dev

---

Preview | Diff