Inventory API: reimplement variation_category
In its current implementation ( introduced in 4787eadd ),
variation_category parameter of Inventory API require movements to be in the
predicate_category table. The approach is to do a first query to get uids of all movements members of the variation and pass their
uid to catalog. My guess is that this does not scale well. It also uses deprecated
where_expression and generates invalid SQL when no movements match.
As far as I know, it is only used in testInventory. We could also consider dropping it, but keeping compatibility is easy.
This implementation just use
Test results are OK; there is one functional test failure but it really looks unrelated.