Java: What is the best way to concat two vectors?

### Describe the usage question you have. Please include as many useful details as possible.

Given two `IntVector`s `one: {1, 2, 3}` and `another: {null, 5, 6}`,
how can I concat them into avector `result: {1, 2, 3, 4, 5, 6}`?

Should I copy element one by one using `copyFromSafe` or is there any convenient method to achieve the same result?

If I should copy element one by one, how can I calculate value count and null count of the result?

```scala
val one : IntVector = ??? // suppose {1, 2, 3,}
val another: IntVector = ??? // suppose {null, 5, 6}

val offset = one.getValueCount() +one.getNullCount() // 3
val len = another.getValueCount() + another.getNullCount() // 3
var i = 0
while i < len do
one.copyFromSafe(i, offset + i, another)
// can I detect whether copied value is null here so that I can respectively count non-null value and null value?
// for example
// val isNull = one.nullAwareCopyFromSafe(i, offset + i, another)
// if isNull then j += 1 else i += 1
i += 1
one.setValueCount(offset + i)
// offset + i is 6, but another may contain null, so value count could be different from actual value.
```

### Component(s)

Java

Commencez par la documentation de l’API IntVector pour copyFromSafe, getValueCount, getNullCount et setValueCount. Déterminez la manière prise en charge de concaténer les deux vecteurs et l’impact des valeurs nulles sur les nombres de valeurs et de valeurs nulles, puis documentez l’approche avec un exemple corrigé pour les entrées indiquées.

Rédigé par le modèle d'indexation à partir du texte de l'issue.