Add a Listbox.OptionGroup component

[JFGagnon]

Using the Listbox component, I was looking for a way to create different groups of item (same thing as the <optgroup> tag). I know it's possible to achieve the same result by just styling and disabling a Listbox.Option component, but I think it would be nice to have a different component to have a clear separation between a "group heading" and the actual options of that group.

The composition could look something like this:

<Listbox>
    <Listbox.Button>My button</Listbox.Button>
    <Listbox.Options>
        <Listbox.OptionGroup title="My first group">
            <Listbox.Option>My option</Listbox.Option>
        </Listbox.OptionGroup>
        <Listbox.OptionGroup title="My second group">
            <Listbox.Option>My option</Listbox.Option>
        </Listbox.OptionGroup>
    </Listbox.Options>
</Listbox>

Keep up the amazing work 👍