Instead of having to repeatedly manually call `onchange_quantity` at
different points in the code, it is better to have it be computed
instead.
- Logic is left unchanged,
- onchange calls from other methods are removed, and
- tests are adjusted to properly handle compute. I.e. remove
'date_planned': datetime.today().strftime(DEFAULT_SERVER_DATETIME_FORMAT)
from when PO lines are created since this sometimes resulted in
inconsistent date_planned values for PO line and the PO date_order
(by 1 sec), which could lead to inconsistently created 'date_deadline'
values for stock_moves' created by PO line qty changes. Issue
previously didn't exist because onchange was not always called.
Part of Task: 2695116 (to avoid adding more onchange calls for new
feature)
Part-of: odoo/odoo#87656
Tiffany Chang (tic)
863c5090f0