[Java] Netty memory release

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

Since when we use netty as my memory allocator manager, I found that direct memory is not released after vector is closed.
```
Field field = new Field("test", FieldType.nullable(new ArrowType.Utf8()), null);
RootAllocator allocator = new RootAllocator(Long.MAX_VALUE);
FieldVector vector = field.createVector(allocator);
for (int i = 0; i < 100000; i++){
((VarCharVector)vector).setSafe(i, "test".getBytes(StandardCharsets.UTF_8));
}

System.out.println("before close memory: " + usedDirectMemory() + " bytes"); //before close memory: 4194304 bytes
vector.close();
allocator.close();
System.out.println("after closed memory: " + usedDirectMemory() + " bytes"); //after closed memory: 4194304 bytes
```
I can address the problem that if the inner allocator `PooledByteBufAllocator` won't free the memory chunk , I am not sure if this is expected.

### Component(s)

Java

RootAllocator、VarCharVector、PooledByteBufAllocatorを使用した提供済みのJava再現コードから始め、続いてallocatorのクローズ動作とNettyのダイレクトメモリ処理を追跡してください。残っている4194304バイトが実際のリークなのか、予期されたプーリング動作なのかを確認し、その結果として期待される動作を文書化またはテストしてください。

索引モデルが issue の本文から書いたものです。