JSON: empty json collection is not correctly materialized, but rather returned as null

[maumar]

related to #29348

even when the json for the collection is set to [] we still materialize it as null. This is because in IncludeJsonEntityCollection we only run fixup code if there is entity in the collection to be fixed up to the parent. And the problem is that the fixup is what generates the collection instance. We should probably have a separate call to generate the collection (when the JSON for it is not null) and run the element fixup independently of the collection creation.

[maumar]

there is also problem for empty json collection inside json mapped entity in the Tracking scenario. In Tracking, we rely on state manager to wire up the json collection to it's parent json entity. Problem is that empty collection is "invisible" to state manager, so the wire-up doesn't happen. It all works fine for NonTracking, since we have to do the wire up ourselves.