[Java] Minor types don't account for nullable FieldType flag

Calling e.g. `FLOAT4.getNewVector("foo", new FieldType(false, ...), ...)" returns a NullableFloat4Vector instead of a Float4Vector.
edit: Float4Vector doesn't implement FieldVector, so can't currently be a top-level vector. I'm confused as to what the nullable flag is supposed to represent then.

**Reporter**: [Emilio Lahr-Vivaz](https://issues.apache.org/jira/browse/ARROW-999) / @elahrvivaz

_{**Note**: *This issue was originally created as [ARROW-999](https://issues.apache.org/jira/browse/ARROW-999). Please see the [migration documentation](https://github.com/apache/arrow/issues/14542) for further details.*}

Comienza en la implementación Java de FLOAT4.getNewVector e inspecciona cómo se interpreta FieldType(false, ...) para Float4Vector y NullableFloat4Vector. Sigue la restricción de FieldVector mencionada en el issue y determina el significado previsto del indicador nullable; se considera terminado cuando el tipo de vector devuelto y el comportamiento del vector de nivel superior coinciden con ese contrato.

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