Update QueryResult design

A query needs to result in a set of path/object tuples, as we really
need to discern matches. Having a concrete path of matches helps
getting identifiers of parent objects for subquent queries.

DOMQueryResult already contains this capability, we just need to
propagate it.

JIRA: MDSAL-604
Change-Id: Iec9ad34aac105eeb45c26a31a24611c9e0f2bb82
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>
(cherry picked from commit eb1359241f3479661b4b317c05b3b2f96e8b6717)