Make available field retrieval be generated through an object

phpcs-errors:221 phpunit-status:successful phpstan-errors:677

public/index3.php

@@ -25,7 +25,8 @@
 
 // Get allowed values * $fieldNoMultiplicator
 $fieldNoMultiplicator = 10;
-require __DIR__ . "/../values/availableFields.php";
+$fieldsGetter = new CsvxmlAvailableFields($lang);
+$availableFields = $fieldsGetter->getFields();
 
 $allowed = $eventpart = $eventpartsure = $fieldsWithDependency = $fieldsWithAllowedValueSet = [];