Add option to use direct queries with AND operator

The query builder only works with "OR". And this will not be changed in Search API Solr.

If you use the direct parse mode, "OR" is also the right choice to have full control over the query. You can achieve "AND" within the query:
+foo +bar means foo AND bar

Automatically closed - issue fixed for 2 weeks with no activity.

Can a maintainer here shed some light on this assertion:

The query builder only works with "OR".

Specifically, can anyone point to specific implementation decisions that led to this limitation? Our client is looking to have "AND" as the default operator, and we'd like to respond to their request with something more constructive than "it's not possible without rewriting a new module". Thanks in advance for your cooperation!