[Java] Avro to Arrow converter doesn't appear to generate valid arrow data

I think this is related to how Unions are handled (I had thought unions of with a null and one other type would get created to the nullable type, but that is a separate issue).

I haven't had time to fully diagnose, but remnants of the code I tried to use are at

And the CSV file from https://issues.apache.org/jira/browse/ARROW-11629?jql=text%20~%20%22arrow%20drill%20parquet%20dictionary%22

produce data that isn't readable by the C++ implementation.

**Reporter**: [Micah Kornfield](https://issues.apache.org/jira/browse/ARROW-12340) / @emkornfield

_{**Note**: *This issue was originally created as [ARROW-12340](https://issues.apache.org/jira/browse/ARROW-12340). Please see the [migration documentation](https://github.com/apache/arrow/issues/14542) for further details.*}

從 Java Avro-to-Arrow 轉換器開始，使用 ARROW-11629 中引用的 CSV 檔案重現問題。檢查連結 gist 中的殘留內容，重點關注 union 處理，然後將產生的資料與 C++ 實作所接受的資料進行比較。當轉換器產生可由 C++ 實作讀取的 Arrow 資料，並為失敗的輸入加入回歸測試時，即視為完成。

由索引模型根據 Issue 內容生成。