Add rooms.required_state to Sliding Sync /sync (#17342)

Also handles excluding rooms with partial state when people are asking for room membership events unless it's `$LAZY` room membership.

tests/test_utils/event_injection.py

@@ -125,13 +125,15 @@ async def mark_event_as_partial_state(
     in this table).
     """
     store = hs.get_datastores().main
-    await store.db_pool.simple_upsert(
-        table="partial_state_rooms",
-        keyvalues={"room_id": room_id},
-        values={},
-        insertion_values={"room_id": room_id},
+    # Use the store helper to insert into the database so the caches are busted
+    await store.store_partial_state_room(
+        room_id=room_id,
+        servers={hs.hostname},
+        device_lists_stream_id=0,
+        joined_via=hs.hostname,
     )
 
+    # FIXME: Bust the cache
     await store.db_pool.simple_insert(
         table="partial_state_events",
         values={