PURPOSE
Since v13 some commits added code in mail thread file. This file is already
quite long and keeping it organized allow to understand its content.
SPECIFICATIONS
Clearly separate CRUD / CRUD HELPERS / TRACKING / ... . Notably tracking
code was split accross two code sections.
Make some internal tools methods private. They do not require to be public
* with_lang: does not makes sense to be available outside of odoo. It is
renamed to _fallback_lang as it does not allow to set a specific lang in
the environment like with_user. It is used to fallback on user's lang
in context;
* get_mail_message_access: purely internal method used for access rights;
LINKS
Task ID-2327096 (code cleaning)
PR #56631
X-original-commit: 4a5fc70cfc3c86da33e2480fbd59c8f6d575c6e9