Make screen reader announce status changes in userlist

[KDSBrowne]

What does this PR do?

This makes the screen reader announce the status changes in the user list so user's don't have to navigate to get the info.

The caveat with this solution is the status notifications are not done through the toasts. For the screen reader this means to announce the status changes, the user-list must be open.

Closes Issue(s)

Closes #11372

[basisbit]

@KDSBrowne can this be disabled or filtered somehow (besides hiding the users list)? I'd imagine otherwise it could be very annoying for blind attendees when there are hundreds of users in the session, and some people join or leave every few seconds?

[KDSBrowne]

@basisbit At the moment there isn't a way to disable apart from closing the user-list. The announcements could surely get annoying if a large number of users continually change their status or join / leave (due to the potential noise).

The element that announces the user is currently set to aria-live="assertive". Changing this to "polite" would make the announcement less intrusive but still probably as annoying. In either case, the screen readers have a shortcut to stop any on going announcement.

Alternatively, a setting could be used to toggle the aria-live property to "off" for disabling.