Return an immutable value from get_latest_event_ids_in_room. (#16326)

changelog.d/16326.misc

synapse/events/builder.py

synapse/handlers/federation_event.py

synapse/storage/controllers/persist_events.py

synapse/storage/databases/main/event_federation.py

synapse/storage/databases/main/events.py

tests/handlers/test_presence.py

tests/replication/storage/test_events.py

tests/replication/tcp/streams/test_events.py

tests/replication/test_federation_sender_shard.py

tests/storage/test_cleanup_extrems.py

tests/test_federation.py