EZP-21700: add language code to SortClause FieldTarget
EZP-21700: add integration tests
EZP-21700: added BC note
Fixed: constructor PHPDoc  description
EZP-21700: make languageCode optional and join with main language
EZP-21700: prevent Field SortClauses with language from filtering Content by language
EZP-21700: added validation of Field SortClauses