Implement phone.getGroupCallJoinAs

[aykutalparslan]

Get a list of peers that can be used to join a group call, presenting yourself as a specific user/channel.

phone.joinAsPeers#afe5623f peers:Vector<Peer> chats:Vector<Chat> users:Vector<User> = phone.JoinAsPeers; ---functions--- phone.getGroupCallJoinAs#ef7c213a peer:InputPeer = phone.JoinAsPeers;