[Java] Avro to Arrow converter should reuse the same VectorSchemaRoot

When originally reviewing the code I suggested a new VectorSchemaRoot on each call to the iterator.  After further discussions on the mailing list, it seems that this is an anit-pattern for working with VectorSchemaRoot, we should update the code to update a single VectorSchemaRoot.

After this change it should be easier to use Avro converter with other components of the library (i.e. filewriter) which also make use of a single VectorSchemaRoot.

**Reporter**: [Micah Kornfield](https://issues.apache.org/jira/browse/ARROW-9613) / @emkornfield

_{**Note**: *This issue was originally created as [ARROW-9613](https://issues.apache.org/jira/browse/ARROW-9613). Please see the [migration documentation](https://github.com/apache/arrow/issues/14542) for further details.*}

Empieza localizando el convertidor Java Avro y su iterador, y luego lee cómo se crea y se devuelve VectorSchemaRoot en cada llamada. El cambio está terminado cuando el convertidor actualiza y reutiliza un único VectorSchemaRoot, lo que le permite funcionar con componentes como filewriter; ejecuta las pruebas existentes del convertidor si están disponibles.

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