Remember the receipt information supplied. For each receipt:
If we don't have the event for this receipt, store it as "dangling" so we can process it later.
Otherwise store it per-user in either the threaded store for its thread_id, or the unthreaded store if there is no thread_id.
Ignores any receipt that is before an existing receipt for the same user (in the same thread, if applicable). "Before" is defined by the unfilteredTimelineSet of the room.
The latest receipts we have for a room.