[FIX] stock_account:make cogs multi_company safe

The aim of this commit is to make the cogs generation multi-company
safe.

2 bugs are fixed in this forwardport commit:
- The product.valuation on the line wasn't evaluated in a company safe
way.
- cogs method weren't company safe either

Before this commit:
- When posting an invoice from company B with both company A and B
selected and A being selected as "main", the cost from company A could
be selected instead of cost from company A to create the anglosaxon
lines.

- If company B's product isn't in real time valuation, cogs aren't even
created.

After this commit:
Whatever the selected companies are, the cost selected will always be from
the company that created the invoice.

closes odoo/odoo#81256

Task: #2686104 and #2713607
X-original-commit: 3f777d43
Signed-off-by: Laurent Smet <las@odoo.com>