Move NXQL comment Elasticsearch hint parser outside of the NXQL parser

Currently we can do NXQL queries like:

SELECT * FROM Document WHERE /*+ES: INDEX(dc:title.ngram) */ dc:title = 'foo'

But the parser for this +ES: functionality is inside the main NXQL parser, even though this is Elasticsearch-specific. This means that anytime we want to change the Elasticsearch hints code, we have to change the main parser. This is not good.

So we should move the Elasticsearch hint parsing outside of the NXQL parser and into Elasticsearch-related code.