Create accessibility menu page

[ichelsea]

Selecting "Accessibility" on the side of the Interface guidelines page is the only section heading that doesn't have a menu. This PR adds in a menu and descriptions as well as rearranges the accessibility side nav links by type (generic or specific) and then by alphabetical order.

This PR adds a menu page for the Accessibility sections.

[vercel]

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🔍 Inspect: https://vercel.com/primer/design/Cn5A7PHqEgkfTvCB7b4EYVD7TATW
✅ Preview: https://design-git-accessibility-menu-page-primer.vercel.app

[ichelsea]

Selecting "Accessibility" from the Interface guidelines menu page gives me a 404 and I can't figure out why 🤔

cc: @simurai

[yaili]

It gives a 404 because it's linking to the live site and that URL doesn't exist yet.

[yaili]

Let me know if you have any questions.

[ichelsea]

Okay, @yaili! This one's ready for your eyes again 🙂

[yaili]

There were a few typos - can you put all the text through a spell checker to make sure nothing was missed? I'm not sure I caught everything.

Also, all the links are broken to the accessibility pages from the Accessibility overview page, so that needs to be fixed too.

[bolonio]

All good (once @yaili's suggestions are done)