Lucene full text: more like this function

[robfrank]

New lucene function (#7155) that perform a more like this query:

SELECT FROM Song where search_more(['#25:2', '#25:3']) = true;

Or with a subquery:

SELECT from Song  let $a=(SELECT @rid FROM Song WHERE author = 'Hunter')  
WHERE SEARCH_More( $a, { 'minTermFreq':1, 'minDocFreq':1} ) = true

MoreLikeThis configuration parameters should be passed as json:

SELECT from Song where SEARCH_More( [#25:2, #25:3] , 
{'fields': [ 'title' ], 
'minTermFreq':1, 
'minDocFreq':1,
'maxWordLen':5
}) = true

All the configuration parameters of MLT should be exposed.

The function will use the MoreLikeThis capability from Lucene itself: https://lucene.apache.org/core/6_5_1/queries/index.html