[FIX]product:change pricelist fixed_price field from float to monetary

steps to reproduce:
-change decimal accuracy for "Product Price"
-create a price list with fixed price
-the fixed price field does not takes the decimal accuracy into account

this was working in V11 and V12
fixed_price was a float field like other price fields

previous behavior:
fixed_price is a monetary field
when setting up a fixed price for a pricelist, it takes into account
the precision from the current currency

current behavior:
fixed_price is a float field
when setting up a fixed price for a pricelist, it takes into account
the proper decimal accuracy setting ("Product Price")

opw-2121964

closes odoo/odoo#40807

X-original-commit: 27b90fc7
Signed-off-by: Jorge Pinna Puissant (jpp) <jpp@odoo.com>

addons/product/models/product_pricelist.py

@@ -449,7 +449,7 @@ class PricelistItem(models.Model):
         ('fixed', 'Fixed Price'),
         ('percentage', 'Percentage (discount)'),
         ('formula', 'Formula')], index=True, default='fixed', required=True)
-    fixed_price = fields.Monetary('Fixed Price')
+    fixed_price = fields.Float('Fixed Price', digits='Product Price')
     percent_price = fields.Float('Percentage Price')
     # functional fields used for usability purposes
     name = fields.Char(
@@ -495,11 +495,12 @@ class PricelistItem(models.Model):
                 item.name = _("All Products")
 
             if item.compute_price == 'fixed':
+                decimal_places = self.env['decimal.precision'].precision_get('Product Price')
                 if item.currency_id.position == 'after':
                     item.price = "%s %s" % (
                         float_repr(
                             item.fixed_price,
-                            item.currency_id.decimal_places,
+                            decimal_places,
                         ),
                         item.currency_id.symbol,
                     )
@@ -508,7 +509,7 @@ class PricelistItem(models.Model):
                         item.currency_id.symbol,
                         float_repr(
                             item.fixed_price,
-                            item.currency_id.decimal_places,
+                            decimal_places,
                         ),
                     )
             elif item.compute_price == 'percentage':