[FIX] orm, product: propagate min_display_digits to related fields

Issue:
---
Record's `min_display_digits` is not inherited in case of a model
inheritance. e.g. `list_price` is inherited to `product.product` from
`product.template`, however it renders with fewer decimals than
`product.template.list_price` in reports.

Steps to reproduce:
1- Set a product's Sales Price to 19.5.
2- Add `product.product.list_price` to a report using studio.

The variant's field renders with 1 decimal while `decimal.precision`
is 2.

Cause:
---
This is missed in ee32a17495a10af18f0b5de0a295283c5059d3c2 which introduces
minimum precision.

opw-6465159

closes odoo/odoo#285607

X-original-commit: 937329b218a89737c96ff4a66f0405b963f60e24
Signed-off-by: Mohammadmahdi Alijani (malj) <malj@odoo.com>
Signed-off-by: Krzysztof Magusiak (krma) <krma@odoo.com>