Rename javascript model `mail.messaging_initializer` to `MessagingInitializer` in order to distinguish javascript models from python models. Part of task-2701674. * = crm_livechat, im_livechat, mail_bot closes odoo/odoo#81387 Related: odoo/enterprise#22889 Signed-off-by: Alexandre Kühn (aku) <aku@odoo.com>