[Java] Support online dictionary builder and encoder

An online dictionary builder and encoder is used for the scenarios where the dictionary is used as is (for some cases, the dictionary may need to be sorted by content or frequency, before encoding).

For such scenarios, the dictionary building and encoding can be performed simultaneously.

**Reporter**: [Liya Fan](https://issues.apache.org/jira/browse/ARROW-6198) / @liyafan82

_{**Note**: *This issue was originally created as [ARROW-6198](https://issues.apache.org/jira/browse/ARROW-6198). Please see the [migration documentation](https://github.com/apache/arrow/issues/14542) for further details.*}

issue 中沒有指出任何 Java 檔案、測試或進入點。首先在 arrow-java 中定位現有的 dictionary builder API 和 encoder API，然後確定如何處理按內容或頻率排序。完成的標準是：對於照原樣使用的 dictionaries，dictionary building 和 encoding 可以同時進行，同時保留所述的排序情境。

由索引模型根據 Issue 內容生成。