as MSC2366 adds an extra interactive step to the verification process,
we can't wait for the verifier after sending the request.

This is a breaking change in the js-sdk as it changes the return type
of an existing method.

so we don't need to import the PHASE_ constants where we need to check

as it's harder to determine the other side of a request, given
the in-room code also processes remote echos for own events.

also put logic to block non-participating senders in VerificationRequest
so it is shared between both channels.

Remote echo's should not be passed to the verifier though.

as once in done, the request is removed from the request map
and the second .done event that comes in will not find the request
anymore, so the request wouldn't be attached to the event anymore,
breaking rendering it in the timeline.

next up is inspecting the .request event to
determine it reliably in InRoomChannel

also fail validation with any event not sent by or directed to us

as it doesn't need to happen for ToDeviceChannel

but doesn't work yet? data where liveEvent is fished out is undefined

this makes the verifier want to interact with the other party
when just reloading the session.

rather than the sender and from_device (which is not always set)

as this was one of the things breaking to_device verification
of ones own devices.

this was one of the things breaking to_device verification

but instead use Promise.resolved() as then always runs in the next tick.

although it doesn't make or break the test

as InRoomChannel looks at this to decide whether an event is
a remote echo (and to pass it to the verifier or not)

which now returns a Promise of VerificationRequest instead of verifier

a request should be accepted by calling accept() on the request.