feat(ui): Add m.room.tombstone to the room list required_state

[Hywan]

This patch adds the m.room.tombstone state event to the list of events in required_state used by the RoomListService. The goal is to offer the possibility for the consumers to know whether a room has been tombstoned or not.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.87%. Comparing base (71abbeb) to head (aad7af3).
Report is 14 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4211      +/-   ##
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- Coverage   84.89%   84.87%   -0.02%     
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  Files         272      272              
  Lines       29142    29142              
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- Hits        24739    24734       -5     
- Misses       4403     4408       +5     

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[kevinaboos]

Echoing my comments from the Matrix Rust SDK room here, as requested:

I tested this PR out in Robrix, but unfortunately was not able to get any tombstoned info at all. Here's what I'm doing, just in case I missed a key step.

When I receive a diff with a new room from the room list service, i then attempt to call several different tombstone-related functions (which I think are all doing mostly the same thing under the hood):

• room.tombstone() always returns None.
• room.get_state_event_static::<RoomTombstoneEventContext>().await also always returns None.
• room.get_state_events(StateEventType::RoomTombstone).await() always returns an empty vec.

i know for a fact that I do have tombstoned rooms on the account that I'm testing with, so I'm expecting them to have tombstoned room state. Here's a side-by-side example showing how both rooms exist as separate rooms in the same session: the new version of Element Web/Desktop on the left, and the old tombstoned one on the right. If I understand tombstoning correctly, I'd expect the old version of the room (on the right) to have a tombstone state event.