[19.0][IMP] pos_sale_picking_keep: Settle ordered quantities even if delivered

[alan196]

When settling a sale order, the PoS deducts the already delivered quantity from each line, because it assumes it will deliver the remaining quantity itself. With this module the sale order pickings are kept and the PoS is only used to charge the order, so lines of already delivered orders were loaded with zero quantity (or even removed for products whose UoM is not groupable in the PoS, due to the line splitting logic of pos_sale).

Load the ordered quantity instead, deducting only the quantity already invoiced to avoid charging twice. Covered with a new tour-based test.

Same change submitted to OCA in OCA#1576 (migration PR, second commit).

Context: reported by Promovago when charging already-delivered sale orders (e.g. C00068) in the PoS.

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[jarsabot]

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