RetrieveUserProfile is a wrapper that queries both the local database and application services for a given user's profile TODO: Remove this, it's called from federationapi and clientapi but is a pure function.

ErrProfileNotExists is returned when trying to lookup a user's profile that doesn't exist locally.

RoomAliasExistsRequest is a request to an application service about whether a room alias exists.

RoomAliasExistsResponse is a response from an application service about whether a room alias exists.

UserIDExistsRequest is a request to an application service about whether a user ID exists.

UserIDExistsRequestAccessToken is a request to an application service about whether a user ID exists.

UserIDExistsResponse is a response from an application service about whether a user ID exists.

AppServiceInternalAPI is used to query user and room alias data from application services.