Implement phone.getGroupCall

[aykutalparslan]

Get info about a group call

phone.groupCall#9e727aad call:GroupCall participants:Vector<GroupCallParticipant> participants_next_offset:string chats:Vector<Chat> users:Vector<User> = phone.GroupCall; ---functions--- phone.getGroupCall#41845db call:InputGroupCall limit:int = phone.GroupCall;