private static List<String> getStructFieldsWithIndex(Collection<? extends ImmutableSDField> structFields) {
        var result = new ArrayList<String>();
        for (var structField : structFields) {
            if (structField.wasConfiguredToDoIndexing()) {
                result.add(structField.getName());
            }
            result.addAll(getStructFieldsWithIndex(structField.getStructFields()));
        }
        return result;
    }
Validates that complex fields (of type struct or map) do not have any struct fields with 'indexing: index'.
This is not supported and will confuse the user if not validated.

Only applies for indexed search clusters.

@author geirst
config-model/src/main/java/com/yahoo/vespa/model/application/validation/ComplexFieldsWithStructFieldIndexesValidator.java