Ensure we do not add relations to the wrong timeline (#3427)

* Do not assume that a relation lives in main timeline if we do not know its parent

* For pagination, partition relations with unknown parents into a separate bucket

And only add them to relation map, no timelines

* Make addLiveEvents async and have it fetch parent events of unknown relations to not insert into the wrong timeline

* Fix tests not awaiting addLIveEvents

* Fix handling of thread roots in eventShouldLiveIn

* Fix types

* Fix tests

* Fix import

* Stash thread ID of relations in unsigned to be stashed in sync accumulator

* Persist after processing

* Revert "Persist after processing"

This reverts commit 05ed6409b3.

* Update unsigned field name to match MSC4023

* Persist after processing to store thread id in unsigned sync accumulator

* Add test

* Fix replayEvents getting doubled up due to Thread::addEvents being called in createThread and separately

* Fix test

* Switch to using UnstableValue

* Add comment

* Iterate

spec/unit/models/thread.spec.ts

@@ -697,7 +697,7 @@ async function createThread(client: MatrixClient, user: string, roomId: string):
 
     // Ensure the root is in the room timeline
     root.setThreadId(root.getId());
-    room.addLiveEvents([root]);
+    await room.addLiveEvents([root]);
 
     // Create the thread and wait for it to be initialised
     const thread = room.createThread(root.getId()!, root, [], false);