[FIX] website_sale: filter fiscal positions on company v2

Sequel of cc54194e.
The mentioned fix only worked when the user was public.

The problem arises when calling the function `_get_fpos_by_region()`
in `sudo` without specifying the company and this happens, for instance,
in every `onchange_partner_*` function of a sale order.

We propose to add the `force_company` key in the context of the sale
order to ensure the right company when selecting the fiscal position.

closes odoo/odoo#31751

Signed-off-by: Rémi Rahir (rar) <rar@odoo.com>