[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.*}

No Java files, tests, or entry points are named in the issue. Start by locating the existing dictionary builder and encoder APIs in arrow-java, then determine how sorting by content or frequency is handled. Done means dictionary building and encoding can happen simultaneously for dictionaries used as-is, while preserving the stated sorting scenarios.

Written by the indexing model from the issue text.