Add EventType::CallMissed and emit it for missed calls (#7840)

[iequidoo]

Before, only CallEnded was emitted for missed calls, or, if a call arrives already being stale,
IncomingMsg. Now:
- CallMissed is emitted in addition to CallEnded.
- IncomingMsg is replaced with CallMissed for stale calls.
Having only one event type for missed calls should simplify handling them in the apps.

This doesn't emit CallMissed for those who aren't allowed to call us. Also, don't emit CallEnded
if the caller isn't allowed to call us and the call wasn't accepted, as there's no previous
IncomingCall event in this case.

Fix #7840

[r10s]

However, maybe CallMissed should only replace IncomingMsg

i think, IncomingMsg was never fired, this is at least the original issue.

and MsgsChanged still needs to be fired, as this is about redrawing the bubble.

but be emitted in addition to CallEnded and not replace it?

yes. CallEnded should not be fired less.

so, CallMissed is fired additionally to CallEnded.

the gist of the three events is different:

• MsgsChanged - refresh the corresponding bubble

• CallEnded - close the call UI

• CallMissed - add a notification about the missed call

so, might be that at the end of the call, all three events are fired. at a first glance, this PR needs adaption.

in other words, this PR should only fire CallMissed additionally, and not remove any other event.

also, deltachat.h needs the event and documentation

[iequidoo]

i think, IncomingMsg was never fired, this is at least the original issue.

It was fired if an already stale call arrives, i replaced it with CallMissed.

and MsgsChanged still needs to be fired, as this is about redrawing the bubble.

Yes, this isn't changed by the PR.

yes. CallEnded should not be fired less.

Now it's not fired less except for the case when the caller isn't allowed to call us and we didn't accept the call because in this case we don't emit IncomingCall as well.

also, deltachat.h needs the event and documentation

Done.