Review a11y for design system and primitive Web Components

As part of #769, a bunch of Web Components have been implemented that may not be completely accessible. In particular, these could be the Menu, Combobox, and Dialog components.

Before looking into this, though, we still have to consider whether we can use 3rd party components from Web Awesome or other libraries. If we do, maybe we can end up removing all the new functionality that has been implemented without an a11y review.

To clarify, the reason why these weren't implemented with full a11y support from the beginning is because doing that requires a lot more work. I preferred to get a basic version going, and once we decide whether we're using 3rd party components or not we can improve them.