Implement EZP-21793: Add $matchAlwaysAvailable parameter to LanguageCode Criterion

This PR resolves issue https://jira.ez.no/browse/EZP-21793

This adds `$matchAlwaysAvailable` parameter to LangaugeCode Criterion, making possible to properly utilize always available flag on the Content level (aka "Use the main language if there is no prioritized translation" option in Legacy administration).