Allow CoreSession.query to return documents from other ids than ecm:uuid

When calling CoreSession.query, doing a SELECT * FROM Document WHERE ... is doing SELECT ecm:uuid FROM Document WHERE ... and returning the documents whose ids are matching.

There are additional use cases of returning documents with other ids, notably in the platform.

1. Direct page provider with SELECT relation:target FROM DefaultRelation WHERE relation:source = ?

2. Simplifying collection management with a query like SELECT collection:documentIds/* FROM Collection WHERE ecm:uuid = ? instead of having a second collectionMember schema on the member documents and doing SELECT * FROM Document WHERE collectionMember:collectionIds/* = ?

Note that in both cases this is still not doing a JOIN, we're first computing a list of ids, then fetching (in batch) the list of documents with these ids.