This update fixes multiple issues in the WhatsApp module including phone number handling, country detection, message formatting, and template validation. The changes improve reliability when sending messages through WhatsApp, especially when dealing with international phone numbers and multi-contact scenarios, while also enhancing the user experience when managing WhatsApp templates and composer functionality.

Purpose of this PR is to aggregate several fixes for the whatsapp module
introduced in 16.3. It also contains some test cleaning, as well as new tests
for fixed issues.

See sub-commits for more details, as there are quite a lot of fixes.

Task-3608129 (Whatsapp: Moultifix !)

Forward-Port-Of: odoo/enterprise#52791
Forward-Port-Of: odoo/enterprise#51001