In the scenario where you have tax excluded from price, when adding
a voucher to an order, we create 2 voucher adjusments. One of them
represent the tax part of the voucher, and has a label starting with
"Tax". To better differentiate them and allow a reliable way to
query it, we add a metadata entry.
It is important that the calculated voucher adjustments don't change
if they are recalculated and it is equally important that they are
updated if the order has changed
It is important that the calculated voucher adjustments don't change
if they are recalculated and it is equally important that they are
updated if the order has changed
It now uses `order.pre_discount_total` to make any calculation, that
means you can call it multiple time and you will still get the same
adjustment amount, included_tax and tax adjustment when needed. This
is assuming nothing changed on the order.
