[FIX] tools.mail: ignore original email during encapsulation

When the system broadcasts an email response to document followers,
if the config parameters `mail.force.smtp.from` or
`mail.dynamic.smtp.from` are defined, it will rewrite the `From`
address to avoid spoofing the sender's domain.

For example, if the `mail.catchall.domain` is set to `example.com` and
an email response comes from:

   "John D" <john@doe.com>

it will rewrite it to:

   "John D (john@doe.com)" <notifications@example.com>

This will make sure the system never sends outgoing email for an external
domain, as it has no authority for doing so, and that could
break mail filtering/authentication rules (SPF, DMARC, etc.)

During this "encapsulation rewrite step", both the original Sender name
and their email are preserved, and put into the quoted "name" field of
the rewritten address. It seems sensible to preserve as much information
as possible about the original sender.

Unfortunately, the inclusion of the Sender email in the final name makes
it appear to some inbox providers as if the message is trying to
deceptively impersonate another person (as many phishing schemes would).
As of November 2021 GMail at least does this, and will hide the name in
the UI when it happens. It will keep only the rewritten email, which is not
very useful in the case of a notification (even though it's more
technically correct, of course).

This patch removes the original email from the rewritten notification,
keeping only the name, considering that the email is not the most
important part, and it's better to have one of the two than none.

So after the patch, the rewritten address is now:

   "John D" <notifications@example.com>

When there is no name in the original address, we keep only the local
part of the email, to avoid the same display issue. The recipient will
have to identify the sender based on the context / past messages.

closes odoo/odoo#79979

Signed-off-by: Olivier Dony <odo@odoo.com>