fix(visitors): Fixes replacing visitor domain. (#14457)

* fix(visitors): Fixes replacing visitor domain.

Constructing the visitor room jid instead of doing a risky replacement.

The problem is having a room like:
[meet-jit-si-shard]someroomname@conference.meet.jit.si and replacing with 'meet.jit.si', the dots match the -.

resources/prosody-plugins/mod_visitors_component.lua

@@ -95,11 +95,13 @@ local function request_promotion_received(room, from_jid, from_vnode, nick, time
  local iq_id = new_id();
  sent_iq_cache:set(iq_id, socket.gettime());
 
+ local node = jid.node(room.jid);
+
  module:send(st.iq({
  type='set', to = req_from, from = module.host, id = iq_id })
  :tag('visitors', {
  xmlns='jitsi:visitors',
- room = string.gsub(room.jid, muc_domain_base, req_from),
+ room = jid.join(node, muc_domain_prefix..'.'..req_from),
  focusjid = focus_jid })
  :tag('promotion-response', {
  xmlns='jitsi:visitors',
@@ -282,11 +284,13 @@ local function process_promotion_response(room, id, approved)
  local iq_id = new_id();
  sent_iq_cache:set(iq_id, socket.gettime());
 
+ local node = jid.node(room.jid);
+
  module:send(st.iq({
  type='set', to = req_from, from = module.host, id = iq_id })
  :tag('visitors', {
  xmlns='jitsi:visitors',
- room = string.gsub(room.jid, muc_domain_base, req_from),
+ room = jid.join(node, muc_domain_prefix..'.'..req_from),
  focusjid = focus_jid })
  :tag('promotion-response', {
  xmlns='jitsi:visitors',