[FIX] sale: fix untaxed_amount_to_invoice field computation

- Go to Invoicing > Configuration > Taxes
- Create a Tax and enable "Included in Price" in Advanced Options tab
- Go to Sales and create a Quotation:
  * Add an Order Line with the created Tax
- Save & Confirm
- Edit the Quotation to set a delivery quantity, then save
- Go to Sales > Reporting > Sales:
  * Display row by "Order #"
  * In Measures, add "Untaxed Amount to Invoice"
- Check the values for the create SO
The amount for "Untaxed Amount to Invoice" is the amount with taxes included.

It is due to the fact that untaxed_amount_to_invoice field of sale.order.line is computed
from price_reduce field.
As price_reduce is computed from price_unit, if there is a tax that is included in the price,
price_reduce will also contain the tax in its value.

opw-2347571

closes odoo/odoo#59297

X-original-commit: 8c54ed42
Signed-off-by: agr-odoo <agr-odoo@users.noreply.github.com>
Signed-off-by: Anh Thao PHAM <kitan191@users.noreply.github.com>