When decrypting the last event for archived rooms when a room key is
received, we used to send a synthetic SyncUpdate. This however put the
archived room into the join section, which converted the room to a
joined room. We need to respect what section the room was in when
sending synthetic SyncUpdates.
fixes https://github.com/famedly/matrix-dart-sdk/issues/1916
BREAKING CHANGE: This changes the runInRoot method to not return a
future. As a user, if you need the result of an async computation passed
to runInRoot, please await it directly. Also the KeyVerification start
and a few call methods now return a future.