[FIX] point_of_sale: allow change lot ids on refund
[FIX] point_of_sale: allow change lot ids on refund

Install POS, create a product available in POS, tracked by Serial
Number.
Add some units of product to the inventory.
Open the POS session, sell the demo item, close the session (do not end
the session, just close the interface).
Go to POS orders, select the last order and click on "Return Products",
the refund will be created with all the products
Edit the refund.

The user will be able to change fields of the refund such as price,
discount, quantity, etc but not the lot ids which will be fixed. Adding
the possibility to edit such field allow to aumatically manage inventory
on refund

opw-2152776

closes odoo/odoo#41905

X-original-commit: 7a02bdda12c161acb5b764866070b83872a7e566
Signed-off-by: Nicolas Martinelli (nim) <771435c469f83f6aa9c405ac5e1ed06314a94f2d@odoo.com>

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