[IMP] base: avoid double formatting in partner 'email_formatted' field

PURPOSE

Be defensive when dealing with email fields, notably when having multi-emails
or email field containing an already-formatted email.

SPECIFICATIONS

Main fix in this commit: fix multiple nested formatting in 'email_formatted'
computation for <res.partner>. Other use cases are mainly left untouched as
we let users deal with their input. In summary :

  * double format: if email already holds a formatted email, we should not use
    it to compute email_formatted, like

      name: Name / email: 'Format' <email@domain.com>
      -> before '"Name" <"Name" <email@domain.com>>"
      -> after '"Name" <email@domain.com>''

  * multi emails: sometimes this field is used to hold several addresses
    like email1@domain.com, email2@domain.com. We currently let this value
    globally untouched by extracting emails and joining them, as we do not
    expect email_formatted to be a list of emails. Extractin emails allows
    to filter out extra text stored in email field, like

      name: Name / email: text, email1@domain.com, email2@domain.com
      -> before: "Name" <text, email1@domain.com, email2@domain.com>
      -> after: "Name" <email1@domain.com,email2@domain.com>

  * invalid email: if something is wrong, better keep it in email_formatted
    than harcoding "False". Indeed this eases management and understanding
    of failures at mail.mail, mail.notification and mailing.trace level. This
    behavior does not change as it was already implemented like that even if
    not sure it was intended;

Task-2612945 (Mail: Defensive email formatting)

Part-of: odoo/odoo#74474