Pawel Domas said:
The conference state field is referring to the current conference in
progress, so it feels like this field should be cleared as soon as we
declare that the conference is being left and the asynchronous process
of leaving the conference starts (which happens on
CONFERENCE_WILL_LEAVE).

Lyubo Marinov said:
Merely setting conference to undefined is incomplete because there are
other redux state properties associated with conference.

What we're doing here is redefining the redux action
CONFERENCE_WILL_LEAVE:

The redux action CONFERENCE_WILL_LEAVE represents the order of the user
to leave a JitsiConference instance. From the user's perspective, there's
no going back (with respect to the instance itself). The app will perform
due clean-up like leaving the associated room, but the instance is no
longer the focus of the attention of the user and, consequently, the app.

Now CONFERENCE_LEFT and CONFERENCE_WILL_LEAVE have more in common than
before and we can do a much better job by expressing the common parts in
source code. Additionally, our source code can be rewritten to better
express the meaning of any of these two actions.

Co-authored-by: Pawel Domas <pawel.domas@jitsi.org>
Co-authored-by: Lyubo Marinov <lmarinov@atlassian.com>