[Java] Add accessors to get type parameters from vector classes

Vector classes contain private copies of each param in the `ArrowType`, but does not have any public api to access them. So if given a vector you would have to get the `Field` from the and cast to the correct type. For example, with a `TimeStampMicroTZVector` and trying to get the timezone:

```

if field.getType.isInstanceOf[ArrowType.Timestamp] &&
field.getType.asInstanceOf[ArrowType.Timestamp].getTimezone
```

It would be more convenient to have direct accessors for these type params for the vector types that have parameters:

- DecimalVector
- FixedSizeBinaryVector
- ListVector
- TimeStamps with timezones
- FixedSizedListVector
- Unions

**Reporter**: [Bryan Cutler](https://issues.apache.org/jira/browse/ARROW-1361) / @BryanCutler
#### PRs and other links:
- [GitHub Pull Request apache/arrow#972](https://github.com/apache/arrow/pull/972)

_{**Note**: *This issue was originally created as [ARROW-1361](https://issues.apache.org/jira/browse/ARROW-1361). Please see the [migration documentation](https://github.com/apache/arrow/issues/14542) for further details.*}

Esamina innanzitutto le classi di vettori menzionate nell’issue e la pull request collegata apache/arrow#972. Controlla come sono rappresentati i loro parametri privati di ArrowType, quindi conferma che esistano accessor diretti per DecimalVector, FixedSizeBinaryVector, ListVector, i vettori timestamp con gestione del fuso orario, FixedSizeListVector e le union.

Scritto dal modello di indicizzazione a partire dal testo della issue.