GH-26597: Also calculate tax discount compensation amount when prices are configured excl. tax

[moloughlin]

This is a fix for the issue raised here: #26597

See: \Magento\Tax\Model\Calculation\AbstractAggregateCalculator::calculateWithTaxInPrice and notice that in this scenario, the calculator does the correct thing for computing compensation value:
$discountTaxCompensationAmount = $rowTax - $rowTaxAfterDiscount;

Meanwhile in: \Magento\Tax\Model\Calculation\AbstractAggregateCalculator::calculateWithTaxNotInPrice the calculation is missing. Tax discount compensation should be calculated regardless of whether catalog prices were provided incl vs excl tax.

[m2-assistant]

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