[REF] mail,hr: move openDMChatWindow to MailManager

It will be used by the Many2OneAvatarUser widget defined in the
next commit.

addons/hr/static/src/js/chat.js

@@ -44,18 +44,8 @@ odoo.define('hr.employee_chat', function (require) {
             open_chat: '_onOpenChat'
         }),
 
-        _onOpenChat: function(ev) {
-            var self = this;
-            var dmChat = this.call('mail_service', 'getDMChatFromPartnerID', ev.data.partner_id);
-            if (dmChat) {
-                dmChat.detach();
-            } else {
-                var def = this.call('mail_service', 'createChannel', ev.data.partner_id, 'dm_chat').then(function (dmChatId) {
-                    dmChat = self.call('mail_service', 'getChannel', dmChatId);
-                    dmChat.detach();
-                });
-                Promise.resolve(def);
-            }
+        _onOpenChat: function (ev) {
+            this.call('mail_service', 'openDMChatWindow', ev.data.partner_id);
         },
     });
 

addons/mail/static/src/js/services/mail_window_manager.js

@@ -52,6 +52,20 @@ MailManager.include({
             }
         }
     },
+    /**
+     * Open a DM chat in a thread window.
+     *
+     * @param {integer} partnerID
+     * @returns {Promise}
+     */
+    openDMChatWindow: async function (partnerID) {
+        let dmChat = this.call('mail_service', 'getDMChatFromPartnerID', partnerID);
+        if (!dmChat) {
+            const dmChatId = await this.call('mail_service', 'createChannel', partnerID, 'dm_chat');
+            dmChat = this.call('mail_service', 'getChannel', dmChatId);
+        }
+        dmChat.detach();
+    },
     /**
      * Open a DM chat in a thread window. This is useful when selecting a DM
      * chatin the blank thread window, so that it replaces it with the DM chat