* feat(screenshare): support remote wireless screensharing

- Pass events to the ProxyConnectionService so it can
  handle establishing a peer connection so a remote
  participant, not in the conference, can send a
  video stream to the local participant to use as a
  local desktop stream.
- Modify the existing start screensharing flow to accept
  a desktop stream instead of always trying to create one.

* adjust ProxyConnectionService for lib review changes