Add DOMDataTreeQueryOperations

Add DOMDataTreeQueryOperations

DOMDataTreeQueryOperations exposes the ability to execute queries
on the backing datastore, much like one would execute a read.

mdsal-binding-dom-adapter is taught to recognize the interface and
use it to offload execution deeper. It still falls back to its
evaluation should the backing store not support this.

DOMStoreReadTransaction gained the ability to value expressions,
using a default implementation based om DOMQueryEvaluator.

Based on that capability, mdsal-dom-broker's transactions are
retrofitted to always provide evaluation locally.

JIRA: MDSAL-607
Change-Id: Ia20acf59870f47c8a84914e239dee82e2a56c1bb
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>