Replaced with types.HeaderedEvent _for now_. In reality we want to move
them all to gmsl.Event and only use HeaderedEvent when we _need_ to
bundle the version/event ID with the event (seriailsation boundaries,
and even then only when we don't have the room version).
Requires https://github.com/matrix-org/gomatrixserverlib/pull/373
Fixes#2863 and makes
```
/upgrade preserves direct room state
local user has tags copied to the new room
remote user has tags copied to the new room
```
pass.
This PR changes the handling of notifications
- removes the `StreamEvent` and `ReadUpdate` stream
- listens on the `OutputRoomEvent` stream in the UserAPI to inform the
SyncAPI about unread notifications
- listens on the `OutputReceiptEvent` stream in the UserAPI to set
receipts/update notifications
- sets the `read_markers` directly from within the internal UserAPI
Co-authored-by: Neil Alexander <neilalexander@users.noreply.github.com>
