[FIX] sale_purchase: adapt POL description

When confirming a sale order, if a purchase order is generated, the
descriptions of the PO's lines won't be adapted to the vendor

To reproduce the issue:
1. Create a vendor V
2. Create a product P:
    - Type: Service
    - In Purchase, add a line L01:
        - Vendor: V
        - Vendor Product Name: Name01
        - Vendor Product Code: C01
    - Purchase Automatically: True
3. Create and Confirm a SO with 1 x P
4. Open the generated PO

Error: The description is incorrect (it's the standard name of P instead
of "[C01] Name01")

OPW-2777702

closes odoo/odoo#86256

closes odoo/odoo#86679

X-original-commit: 77a2ad4b81c54fe6a91f2be242345c9d2af10dc0
Signed-off-by: Tiffany Chang <tic@odoo.com>
Signed-off-by: Adrien Widart <awt@odoo.com>