Update /whoami response to match Spec v1.2 (#2201)
Update /whoami response to match Spec v1.2 (#2201)

Basically include `is_guest` and `device_id`. The latter is
needed for https://github.com/matrix-org/complement/pull/305
matrix-org/dendrite,matrix-org/dendrite,matrix-org/dendrite,matrix-org/dendrite