Typeahead does not fully follow WAI-ARIA spec

[rgossiaux]

The WAI-ARIA spec for Listbox mentions (emphasis mine):

Type a character: focus moves to the next item with a name that starts with the typed character.

However, as reported by a user on Reddit, Headless UI does not do that; instead, we search for the first item with a name that starts with the typed character. You can see this in action on https://headlessui.dev/react/menu by repeatedly typing the letter d (with pauses in between). This affects Listbox and Menu both.