[Java][Docs] Document the use of the batchSize argument in Dataset ScanOptions

Several ScanOptions methods take a batchSize argument as shown: 

`public ScanOptions(long batchSize) {`
`    this(batchSize, Optional.empty());`
``}

Since the scanner reads one ArrowRecordBatch per load invocation, setting the parameter to a size larger than the RecordBatch has no effect. It only works when it's smaller than the number of rows in the RecordBatch, (i.e., the number or records read is equal to min(batchSize, recordBatch rowCount), potentially leading to some confusion. 

**Reporter**: [Larry White](https://issues.apache.org/jira/browse/ARROW-17346) / @lwhite1

_{**Note**: *This issue was originally created as [ARROW-17346](https://issues.apache.org/jira/browse/ARROW-17346). Please see the [migration documentation](https://github.com/apache/arrow/issues/14542) for further details.*}

从接受 batchSize 的 Dataset ScanOptions 方法开始，追踪扫描器如何在每次调用时加载一个 ArrowRecordBatch。记录值大于 RecordBatch 行数时不会产生额外效果，而较小的值会将记录数限制为 min(batchSize, recordBatch rowCount)；当 ScanOptions 文档明确说明这一行为时，即表示完成。

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