[IMP] base: add format to res.currency

`res.currency` already has some utilitises like `round` or
`compare_amounts` but until now we always needed to import
`format_amount` from the tools in order to format.

This commit unifies the API.

X-original-commit: 3517a0fece96dd5d0deb02c9fd973444e748986b
Part-of: odoo/odoo#117964

odoo/addons/base/models/res_currency.py

@@ -188,6 +188,17 @@ class Currency(models.Model):
                         )
         return amount_words
 
+    def format(self, amount):
+        """Return ``amount`` formatted according to ``self``'s rounding rules, symbols and positions.
+
+           Also take care of removing the minus sign when 0.0 is negative
+
+           :param float amount: the amount to round
+           :return: formatted str
+        """
+        self.ensure_one()
+        return tools.format_amount(self.env, amount + 0.0, self)
+
     def round(self, amount):
         """Return ``amount`` rounded  according to ``self``'s rounding rules.