When ThreadListService is created it now immediately spawns a background
task (via the client's TaskMonitor) that subscribes to the room event
cache and listens for RoomEventCacheUpdate::UpdateTimelineEvents.
For every incoming event that carries an m.thread relation pointing to a
root we are already tracking, the service rebuilds a ThreadListItemEvent via the
existing build_latest_event helper and replaces latest_event on the matching
ThreadListItem and increments num_replies by 1
Stefan Ceriu
1dd413e4bc