Adapt to new DM definition changes in the SDK (#6748)
* Set `DmRoomDefinition.TwoPeople` in `ClientBuilder`. This applies the 'direct and with at most 2 non-service members' rule to what the SDK should consider a DM.
* Map `RoomInfo.isDm` from the SDK
* Map `NotificationData.isDm` from `NotificationInfo.roomInfo.isDm`
* Remove `RoomIsDmCheck` file as its extension functions are now redundant. Move `Room.isDm` helper function to `BaseRoom`.
* Map `isDm` in `SpaceRoom` from the SDK too
* Replace `isDirect` with `isDm` where possible
* Map `RoomMember.isServiceMember` from the SDK and use it to tell apart normal members of a room from service members (i.e. `RoomMembersState.getDirectRoomMember`)
