Activity-level feedback method accepts attachment_ids but not its mixin-level
counterpart. This commit fixes that by adding the parameter. The activity-level
action_feedback_schedule_next method now also accepts attachments in addition
to the feedback, making the API coherent through all entry points.
At activity level ``action_done`` now goes through ``action_feedback``. This
means it now has two main methods
* ``action_feedback``;
* ``action_feedback_schedule_next``;
All methods finally end up calling ``_action_done`` and correctly propagate
feedback and attachments. We have a bit less entry points with possible API
changes.
Test mail models are updated to be able to use this small addition.
Task-2710804 (Mail: Clean MailThread API)
Part-of: odoo/odoo#86393
Thibault Delavallée
c2fd9a4965