d5c0e209fc
This patch moves the `Room::display_name()` method, and all the siblings, into a new `display_name` module. It includes types like `RoomDisplayName`, `UpdatedRoomDisplayName`, `RoomSummary` etc. This patch also moves the tests in this new module. The idea is to group `Room` API by “theme” in modules, to clarify the code and to make the big `rooms::normal` module smaller.