[Java] Avro to Arrow converter doesn't appear to generate valid arrow data

I think this is related to how Unions are handled (I had thought unions of with a null and one other type would get created to the nullable type, but that is a separate issue).

I haven't had time to fully diagnose, but remnants of the code I tried to use are at

And the CSV file from https://issues.apache.org/jira/browse/ARROW-11629?jql=text%20~%20%22arrow%20drill%20parquet%20dictionary%22

produce data that isn't readable by the C++ implementation.

**Reporter**: [Micah Kornfield](https://issues.apache.org/jira/browse/ARROW-12340) / @emkornfield

_{**Note**: *This issue was originally created as [ARROW-12340](https://issues.apache.org/jira/browse/ARROW-12340). Please see the [migration documentation](https://github.com/apache/arrow/issues/14542) for further details.*}

Comienza con el conversor Java Avro-to-Arrow y reproduce el problema utilizando el archivo CSV referenciado desde ARROW-11629. Revisa los restos del gist enlazado, centrándote en el manejo de union, y después compara los datos generados con lo que acepta la implementación de C++. Se considera terminado cuando el conversor produzca datos de Arrow legibles por la implementación de C++, con una prueba de regresión para la entrada que falla.

Escrito por el modelo de indexación a partir del texto del issue.