[17.0] sale_fixed_discount: Online Preview doesn't show discounted unit price

[kwoychesko]

I'm happy to work on this issue myself (love this module! Thank you for your work including the big refactor!) But I just wanted to be sure nobody was working on it already.

Module

sale_fixed_discount

Describe the bug

If sale_fixed_discount is not installed and a % discount is applied to a product the online Preview (e.g. using the Preview button on the sale order) shows the regular unit price in red with strikethrough and the new discounted price shown below in black. If sale_fixed_discount is installed, the "new discounted price" is just the old regular price.

To Reproduce

Affected versions: 17.0

Steps to reproduce the behavior:

1. In a runboat.odoo-community.org instance for sale-workflow, login and enable Discounts in the Sales general settings.
2. With sale_fixed_discount installed, create a new quotation.
3. Add a product (e.g. Acoustic Bloc Screens with a unit price of $295).
4. In the line’s Disc.% column, enter 50.
5. Click Preview (the portal/online preview view).
   Expected behavior
   The strikethrough price should be $295.00 and the replacement price should be the discounted unit price, $147.50—just as in the preview when sale_fixed_discount is not installed. Instead, the non-discounted unit price is shown.