[FIX] mrp: reserve raw SM with specific lot

On tablet view, if the user selects another lot than the one
reserved, we will still keep a reservation for the old one

To reproduce the issue:
(Need mrp_workorder)
1. Create two products P_finished, P_compo:
   - Storable
   - Tracked by SN
2. Update on hand quantity of P_compo:
   - 1 x SN01
   - 1 x SN02
   - 1 x SN03
3. Create a BoM:
   - Product: P_finished
   - Components: 1 x P_compo
   - Operations: 1 x a new operation
4. Create, confirm and assign a MO for 2 x P_finished
5. Start the WO
6. Set a finished lot
7. The consumed lot is SN01, set it to SN03
8. Validate the WO
9. Mark WO as done
   - Do not close the MO
10. Open the detailed operations of the MO

Error: There is a line that consumes SN03, but there is also a line
for SN01's reservation. This is incorrect, while the MO is not
closed, the quant of SN01 has its available quantity equal to 0.

Since we have to create a backorder, we split all SM. Then, we
remove the excess reservation. To do so, we unreserve the raw SM and
then assign it again. Here is the issue: we run the generic assign
process, so it will not consider that there is already a SML with a
done quantity, i.e.: it will ignore the consumed lot and will just
try to reserve the first one it finds (-> SN01)

OPW-3104930

closes odoo/odoo#110400

Related: odoo/enterprise#36033
Signed-off-by: Arnold Moyaux (arm) <arm@odoo.com>