Searching multiple words gives less results than it used to

Since XWIKI-14938 multi search relevancy works differently and tend to provide AND as default behaviour. To widen the search as it was possible on pre 10.1 instance is more difficult.

Steps to reproduce on two instance with the same database:

• on a pre-10.1:
  • foo bar = 1000 results
  • foo OR bar = 1000 results
  • foo AND bar = 17 results
  • +foo +bar = 17 results

• On XWiki 10.1 or later version:
  • foo bar = 17 results
  • foo OR bar = 17 results
  • foo AND bar = 17 results
  • +foo +bar = 17 results