New threads are not properly shown in the Main Timeline (room)

[Palid]

Steps to reproduce

1. Login with two different accounts and join the same room (Alice and Bob)
2. Write a message from any of those account (Bob)
3. Create a thread with the same account (Bob)
4. Expect that on the second account (Alice) you will have the message with a thread

Outcome

What did you expect?

A threaded message, as the Bob account created

What happened instead?

The thread was not created

Problems analysis:

1. EventTile.tsx is not properly listening for thread events updated, see: Fix threads not rendering properly in main timeline matrix-org/matrix-react-sdk#6929 (this pull request on itself does not fix the problem, as model is broken)
2. matrix-js-sdk/src/models/thread.ts:77 - the root is always overriden when getting a new thread with the first reply event, instead of the actual thread's root.
3. The proper root event (which in this case would be event.replyEventId, matrix-js-sdk/src/models/thread.ts:77) has not been added to the Thread's timeline, which means that event.rootEvent never exists and threads can't render

Operating system

No response

Browser information

No response

URL for webapp

No response

Homeserver

No response

Will you send logs?

No

[Palid]

This issue is also responsible for threads sometimes not rendering properly in the main timeline on initial sync.

[germain-gg]

To test again after matrix-org/matrix-react-sdk#6949 lands

[germain-gg]

Fixed as part of matrix-org/matrix-react-sdk#6952