Track a11y test count

[nwmac]

Summary

Fixes #16430

Occurred changes and/or fixed issues

This is a small improvement which changes the format of the custom accessibility json we generate so it includes some of the stats in terms of the number of accessibility tests we have. This is support future work to keep track of tests, accessibility etc.

Checklist

• The PR is linked to an issue and the linked issue has a Milestone, or no issue is needed
• The PR has a Milestone
• The PR template has been filled out
• The PR has been self reviewed
• The PR has a reviewer assigned
• The PR has automated tests or clear instructions for manual tests and the linked issue has appropriate QA labels, or tests are not needed
• The PR has reviewed with UX and tested in light and dark mode, or there are no UX changes
• The PR has been reviewed in terms of Accessibility
• The PR has considered, and if applicable tested with, the three Global Roles Admin, Standard User and User Base

[rak-phillip]

If I understand correctly, we shouldn't see any changes to the generated report output at this time. Is that right?

[nwmac]

Yes, no changes. The html is the same. The json format changes slightly, but this is not currently used - but it will be going forward.

[rak-phillip]

LGTM