Allow hosts to remove a guest from their session at any time

[lostintangent]

When a guest joins a collaboration session, the host receives a notification that also includes the ability to remove that user. However, as soon as the host dismisses a join notification, they no longer have a way to remove the corresponding user from the session (which is a little awkward). In order to provide hosts with complete control over their guest list, without requiring them to retain join notifications for every guest, we should introduce a simple way to kick out a user at any time (e.g. a new “Remove Guest” command in VS Code, a “Remove Guest” context menu item associated with the user avatar in VS).

As suggested by #342, this action should likely result in the user being “blocked”, so that they couldn’t immediately re-join the session after being removed. Otherwise, the host would potentially need to keep removing a misbehaving user. I’d love to hear feedback on this behavior from folks, as well as what the right name for this action should be (e.g. block, kick, remove?)

[lostintangent]

We just shipped an update that includes a new VS Live Share explore view. Among other things, this displays the set of participants, and allows you to remove any of them from the session 🚀