Multiselect listbox missing some recommended keyboard shortcuts

[rgossiaux]

What package within Headless UI are you using?

Either

What version of that package are you using?

insiders

What browser are you using?

Chrome

Reproduction URL

Vercel build from your repo: https://headlessui-react-5g4ofjz7h-tailwindlabs.vercel.app/listbox/multi-select

Describe your issue

The WAI-ARIA 1.2 Authoring Practices have some recommended keyboard shortcuts for multi-selection which haven't been added--stuff like Ctrl-A to select every option and Shift-Up/Down to focus+toggle the previous/next option. You might want to consider adding them before release.