feat(macros): add Accessibility sidebar

[estelle]

Summary

New sidebar for the accessibility section

Problem

There is no sidebar for accessibility. Instead, each page has a variation of:

<section id="Quick_links">
  {{ListSubpagesForSidebar("Web/Accessibility", 1)}}
</section>

Solution

This is a new sidebar for that section. English only, but localization is possible.

Screenshots

Before

After

How did you test this change?

local build. new page.

[estelle]

[estelle]

https://github.com/mdn/content/pull/32818 is dependent on this PR being merged

[estelle]

Hi @caugner. This is ready for a re-review and, hopefully, a merge. Thanks.

[OnkarRuikar]

• @caugner could you expedite mine too? Which is similar: https://github.com/mdn/yari/pull/10679

[caugner]

Thank you @estelle, great job! 🙌