NativeDatasetFactory parameter allocator and memory pool relationship

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

@zhztheplayer
```
/**
* Constructor.
*
* @param allocator a context allocator associated with this factory. Any buffer that will be created natively will
* be then bound to this allocator.
* @param memoryPool the native memory pool associated with this factory. Any buffer created natively should request
* for memory spaces from this memory pool. This is a mapped instance of c++ arrow::MemoryPool.
* @param datasetFactoryId an ID, at the same time the native pointer of the underlying native instance of this
* factory. Make sure in c++ side the pointer is pointing to the shared pointer wrapping
* the actual instance so we could successfully decrease the reference count once
* {@link #close} is called.
* @see #close()
*/
public NativeDatasetFactory(BufferAllocator allocator, NativeMemoryPool memoryPool, long datasetFactoryId) {
this.allocator = allocator;
this.memoryPool = memoryPool;
this.datasetFactoryId = datasetFactoryId;
}
```

what's the relationship between allocator and memoryPool, does allocator allocate buffers from the memory pool or there is no such restrictions?

thanks

### Component(s)

Java

issue に示されている NativeDatasetFactory コンストラクターから始め、BufferAllocator と NativeMemoryPool がどのように使用されているかを追跡します。Java API ドキュメントでそれらの関係を明確にし、ネイティブ割り当てパスから contributors が検証できる内容も含めます。使用方法に関する疑問に明確な答えが出れば完了です。

索引モデルが issue の本文から書いたものです。