Improvement EZP-22191: Change Criterion\LanguageCode to match alwaysAvailable content by default
Improvement EZP-22191: New \$useAlwaysAvailable argument for ContentService methods with language filtering

The bahavour is not enabled by default in this commit as this is meant for backports.
BC break when changing the default is that any code expecting to get exception when
not a specific translation exists will break if content is always avaiable and main
language is something else then what code is asking for.
Improvement EZP-22191: Change $useAlwaysAvailable arguments in ContentService to true by default
Improvement EZP-22191: Change SearchService to pass languages & useAlwaysAvailable $fieldFilters to ContentService