Disabled options at the end/beginning of list are accidentally hidden from ArrowDown/ArrowUp events

[calthomson]

A minor-ish bug, but something that I personally will need to find a workaround for, so I thought I'd mention it here!

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When a Combobox.Option is disabled, it is no longer selectable. If the disabled Combobox.Option is at the top or bottom of the Combobox.Options list, it becomes unreachable/invisible when using only ArrowDown/ArrowUp because we cannot ArrowDown/ArrowUp to scroll down/up to see it, since ArrowDown/ArrowUp only controls selection, and the element can't be selected. It can be seen if you explicitly scroll.

To recreate:

1. Take a situation like here: https://headlessui-react-git-multi-value-support-tailwindlabs.vercel.app/combobox/multi-select -- but include enough input options that they overflow the box so you have to scroll to see the ones at the end of the list.
2. Give the input option at the end of the list disabled={true}
3. Try to view all elements in the list by ArrowDown/ArrowUp key events alone.

Expected: Even though the disabled input option is not selectable, I still expect to be able to "page down" through the list via ArrowDown events.

Actual: I cannot page down past the second-to-last input option (the last non-disabled input option), making it seems as if that is the end of the list. I can still explicitly scroll down.

This also occurs when the disabled input option is at the top of the list. If you scroll down out of view of that option, then try to go back up to see it again, it will be impossible to view again since it can't be selected.