Enable escape of '*' character in MatchPhrasePrefix ES queries

It is not possible to escape the "*" wildcard character in Elasticsearch-enabled NXQL queries, making it impossible to make specific MatchPhrasePrefix queries on terms that use the character.

Steps to reproduce:

1. Configure ES indexing to enable ILIKE queries on some test field (e.g. dc:title, or a String field from a custom schema)
2. Add nxql_search to the list of page providers in elasticsearch.override.pageproviders in nuxeo.conf
3. After starting nuxeo, create a set of documents with varying values for the term:
   -TestWild
   -TestWild*
4. Add the following term to the query (attempting to escape '*' character) and run search:

   AND [testproperty] ILIKE 'TestWild\\*'
   

Expected Result:
Query returns one result with 'TestWild*' value

Actual Result:
Query returns all entries beginning with 'TestWild', as if '*' character was not escaped