Implement phone.getGroupParticipants

[aykutalparslan]

Get group call participants

phone.groupParticipants#f47751b6 count:int participants:Vector<GroupCallParticipant> next_offset:string chats:Vector<Chat> users:Vector<User> version:int = phone.GroupParticipants; ---functions--- phone.getGroupParticipants#c558d8ab call:InputGroupCall ids:Vector<InputPeer> sources:Vector<int> offset:string limit:int = phone.GroupParticipants;