[EuiSelectable] Screen reader arrow navigation experience is broken on Safari+VO

[cee-chen]

This is reproducible on the baseline EuiSelectable component on production: https://eui.elastic.co/#/forms/selectable

Note how when navigating down/away from an item, it re-announces the previous item and its state, but does not announce the new item's state until it's navigated away from.

Originally posted by @cee-chen in #7715 (comment)

Several other notes:

• Not broken on Firefox+VO
• Fully working in JAWS+NVDA
• It is very unclear whether the issue is with our markup or Safari itself 😞

[JasonStoltz]

At this point, we're not totally sure what we can do here, but we did want to have this tracked in the EUI repository as a known issue.

We're not sure that there's actually anything we can do on our end, we suspect that this is an issue in Safari. If we can find a related but for Safari that we can link here, we will. We're going to add the "blocked" tag for now indicate this.