[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 中没有指出任何 Java 文件、测试或入口点。首先在 arrow-java 中定位现有的 dictionary builder API 和 encoder API，然后确定如何处理按内容或频率排序。完成的标准是：对于按原样使用的 dictionaries，dictionary building 和 encoding 可以同时进行，同时保留所述的排序场景。

由索引模型根据 Issue 内容生成。