DenseUnionVector is not transferred correctly

### Describe the bug, including details regarding any error messages, version, and platform.

Hello,

I encountered a weird issue when converting a `Table` to a `VectorSchemaRoot`. All the `DenseUnionVector` were empty after the conversion.
From my understanding, it looks like there is a bug in the `TransferImpl.transfer` method of the `DenseUnionVector`.
After copying the `valueCount` value to the second vector [in this line](https://github.com/apache/arrow/blob/45918a90a6ca1cf3fd67c256a7d6a240249e555a/java/vector/src/main/codegen/templates/DenseUnionVector.java#L634), it should also set the `nextTypeId`.
After the transfer, `nextTypeId` is equals to `0`, so trying to transfer again would create an empty vector as [the for loop is done against the `nextTypeId`](https://github.com/apache/arrow/blob/45918a90a6ca1cf3fd67c256a7d6a240249e555a/java/vector/src/main/codegen/templates/DenseUnionVector.java#L628)

Proposed fix would be as simple as :

```java
@Override
public void transfer() {

...

for (int i = 0; i < nextTypeId; i++) {
if (internalTransferPairs[i] != null) {
internalTransferPairs[i].transfer();
to.childVectors[i] = internalTransferPairs[i].getTo();
}
}
to.valueCount = valueCount;
to.nextTypeId = nextTypeId;
clear();
}
```

I will raise a PR with the change.

### Component(s)

Java

Inizia in java/vector/src/main/codegen/templates/DenseUnionVector.java, in particolare in TransferImpl.transfer e nel ciclo che usa nextTypeId. Riproduci la conversione da Table a VectorSchemaRoot e verifica che un DenseUnionVector trasferito mantenga il proprio numero di valori e lo stato dei tipi, in modo che un trasferimento successivo non sia vuoto.

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