[IMP] mrp: Do not write quantity done on draft line

In the backorder process the operation are done in this order:
1. If the MO has workorders then set the remaining quantity as quantity
producing
2. Confirm the moves

However the system do not expect qty done on draft moves for a lot
of operations.

This commit inverse the order to allow some buisness logique to work
(e.g the analytic accounting)

opw-2469742

closes odoo/odoo#68708

Related: odoo/enterprise#18594
Related: odoo/upgrade#2739
Signed-off-by: Arnold Moyaux <amoyaux@users.noreply.github.com>