[FIX] account: fix tax basis display on report

Activate multicurrency. The default currency for the company should be
USD. Make an invoice in EUR, with taxes, save and create the invoice.

The tax section will display the correct tax amount but the displayed
amount on which the tax should be applied is wrong: it's displayed the
amount in the company currency rather than the invoice currency.

Adding a _convert step to restore the correct currency since that
information does not appear to be saved in the database

opw-2161039

closes odoo/odoo#42494

X-original-commit: f9a8015ef8231a23cf8e5552c08248cfc95e977c
Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>

addons/account/models/account_move.py

@@ -1272,8 +1272,12 @@ class AccountMove(models.Model):
                 res[line.tax_line_id.tax_group_id]['amount'] += line.price_subtotal
                 tax_key_add_base = tuple(move._get_tax_key_for_group_add_base(line))
                 if tax_key_add_base not in done_taxes:
+                    if line.currency_id != self.company_id.currency_id:
+                        amount = self.company_id.currency_id._convert(line.tax_base_amount, line.currency_id, self.company_id, line.date)
+                    else:
+                        amount = line.tax_base_amount
+                    res[line.tax_line_id.tax_group_id]['base'] += amount
                     # The base should be added ONCE
-                    res[line.tax_line_id.tax_group_id]['base'] += line.tax_base_amount
                     done_taxes.add(tax_key_add_base)
             res = sorted(res.items(), key=lambda l: l[0].sequence)
             move.amount_by_group = [(