Polymorphic "derivedFrom" definition for derived properties

See https://discourse.hibernate.org/t/indexingdependency-for-abstract-method/4996/5

In some cases, an abstract property is mapped to a field, and that property is derived differently in each concrete type.

We should be able to define @IndexingDependency(derivedFrom = ...)) differently for each concrete type.

Some quick testing reveals that it already works for properties at the root of an indexed entity, but I suspect it won't work when the derived property is in an @IndexedEmbedded. We should test that and make it work.

I started implementing some tests here: