Purpose of this commit is to prepare ground for future improvements by already
supporting QWeb rendering in ``mail.render.mixin``.
We temporarily support new field parameters allowing to tune the rendering
directly from field. Notaby choosing engine (jinja or qweb) can be done
from field directly. This is considered as experimental, used mainly to
prepare QWeb support.
Task ID-2534550 (Template usage improvement)
Task ID-2477164 (Composer mixin)
Prepares Task ID-27033 (QWeb in templates)
COM PR odoo/odoo#70889
ENT PR odoo/enterprise#18352
Thibault Delavallée
69dfaf4ca5