This is a sub-ticket of #816 to discuss the outline for a new Accessibility chapter for the Theme Handbook.

The initial outline for this chapter is in the outline Google Doc, but this was really rough and based on the existing pages:

• https://developer.wordpress.org/themes/functionality/accessibility/
• https://developer.wordpress.org/themes/block-themes/accessibility/

For this ticket, we can use it to discuss a better outline and to coordinate any work. The ultimate goal during the planning phase for the handbook overhaul was to have a chapter specifically dedicated to accessibility, but I'm open to whatever structure everyone thinks is best.

@amberhinds and @joedolson have volunteered to help push this documentation forward.