* Make the embedded mode screen sharing a request-each-way rather
than request-and-reply, since replies time out and so can't wait
for the user.
* Try normal screen sharing first, then fall back to using the widget
API if it fails (for lack of a good way of detecting when we
should be using the widget API).
Fixes https://github.com/vector-im/element-call/issues/649
This will probably be overly sensitive until we start timing out
member events (ie. https://github.com/matrix-org/matrix-js-sdk/pull/2446
lands) because lots of calls might have old member events from people
who've joined previously.
