[FIX] sale_stock: lot number not shown in refund invoices

This commit is to compute correct lot number for serial/lot tracked
products on refund invoices

Reproduction:
1. Install Sale, Accounting, Inventor. In setting of Inventory, enable
Lots & Serial Numbers, Display Lots & Serial Numbers on Invoices,
Display Lots & Serial Numbers on Delivery Slips.
2. Create a product with lot/serial number
3. Create a order of this product, confirm. Click the delivery and
validate it.
4. Back to the SO, create an invoice, confirm and print it, the serial
number shows.
5. At the invoice, click “Add credit note”, choose “Full refund” (2
invoices for the SO) or “Full refund and new draft invoice” (3 invoices
for the SO), the lot number doesn’t show in new draft invoice or the
refund invoice

Reason: the current lot number tracking workflow focused on invoicing
different numbers of products and making sure it gets the correct
lot/serial number. It doesn’t include the refund invoice case.

Fix: since the current working logic works great with invoicing products
which are delivered from the warehouse to the customer, we can reuse
this logic for refund invoices for products which are returned from the
customer to the warehouse. In the refund and return case, we switch the
calculation of warehouse and customer. Thus, a return can be seen as a
delivery from the customer to the warehouse.
In the code, we set a new variable, return_source_usage, to check if the
account move type is a delivery or a return. If it’s an invoice for
return, we take the opposite of the previous invoiced product quantity.
Because in a refund, previous invoiced is now considered as refunded.
In the original workflow, when sml.location_id.usage is “customer”, it’s
a return and we update the returned_qty and the related quantities. In
the new workflow, if the invoice is a refund one, we do the same steps
when sml.location_id.usage is “internal”, e.g. when the stock move line
is a delivery, we consider it a return.

For refund invoices. There are two choices of refunding:
1. refund and a refunding invoice: 2 invoices for the order, one is the
original one, another is the refund
2. refund and create a new draft invoice: 3 invoices for the order,
original one, a new draft one and the refund.

In the second case, we will create a new draft invoice. If we simply
apply the original work logic, the lot number will not be printed on the
draft invoice. This is because the previous amls list includes its
original invoice. We have to filter out the duplication of the same
invoice to print the right lot number for the new draft invoice.

Added the report test for two refund cases, one for cancel (Full refund)
and another for modify (Full refund and new draft invoice)

opw-2879714

closes odoo/odoo#99691

Signed-off-by: Laurent Smet <las@odoo.com>