Screen readers should not announce current time every time a new message is received

[pafcu]

Description

Currently Riot permanently shows the time of the last message in the timeline (for other messages this is only shown on hover). This is fairly annoying with a screen reader as it means that the current time is announced every time a new message arrives. We could probably hide this information from screen readers.

We may also need to figure out how to show timestamps on request using something else than hover (e.g. show on some specific keypress).

Steps to reproduce

• Start orca screen reader
• Create a new room
• Invite riot-bot
• Trigger the tutorial
• Observe that you now definitely know what time it is

Version information

Riot web c28d9e5-react-c002d3ff9967-js-36ff0ad0193e on FF57 and orca 3.26.0

[turt2live]

Brief research tells me this might be solvable with aria-live.

[pvagner]

I think the same thing would also fix #5697.
The thing is we do currently have aria-live set to polite on the outer time line div hoping screen readers would automagically anounce new events as they arrive.
However now with these two bug reports it's apparent this is not very nice strategy although some casual screen reader users like me might be fine overlooking this issue all the time.
With the current state screen readers do read all the changes to the time line if the place which has just been changed is visible.
I am thinking that the fix here might be

• Remove the aria-live from the outer div.
• Only set aria-live conditionally just when appending new messages.

This way aria-live won't be kicking in even when scrolling.

[pvagner]

I haven't yet tested this but now when looking at the ScrollPanel and TimelinePanel components I think we should use the same strategy these components are using for when to push content. They are only adding new events to the end if the ScrollPanel is stuck at bottom.

[Palid]

Related #5679