Deduplicate NodeIdentifierWithPredicate/LeafNode values when writing streams

This is a follow-up on CONTROLLER-1908, where we should understand where a LeafNode inside a MapNode corresponds to a key and thus has had its value emitted as part of the NodeIdentifierWithPredicates – these are expected to always match.

While CONTROLLER-1908 deals with the memory footprint of data restored from the stream, this issue is about not emitting duplicate values (or even QNames) for leaves that are covered in the predicates.