Use room_stats_state.room_type column instead of fetching m.room.create event

[squahtx]

#13031 introduced a room_type column in room_stats_state. There are now one or two places where we can avoid fetching m.room.create events and just use the new column instead.

Searching for EventContentFields.ROOM_TYPE or "room_type" ought to find them all.

eg. if we make get_room_with_stats return room_type, we can avoid fetching the m.room.create event in RoomSummaryHandler._build_room_entry.

[clokep]

We do need to wait until the background update finishes, however. I'm unsure if we have a standard way of doing that?

[clokep]

eg. if we make get_room_with_stats return room_type

Looks like #13208 already did this part! 🎉