EZP-21893: Handle LanguageCode criterion $matchAlwaysAvailable parameter in Solr storage visitor

This PR resolves issue https://jira.ez.no/browse/EZP-21893

Title says it all.
Different scores come from different number of content found in a single language. For example 1 of 16 content found in eng-GB makes a lower score than 1 of 2 content found in eng-US.

Sub-task of https://jira.ez.no/browse/EZP-21897.