[Java] Transfer validity buffer data word at a time (currently we do byte at a time)

We should split and transfer validity buffer contents word at a time.

**Reporter**: [Siddharth Teotia](https://issues.apache.org/jira/browse/ARROW-1876) / @siddharthteotia

_{**Note**: *This issue was originally created as [ARROW-1876](https://issues.apache.org/jira/browse/ARROW-1876). Please see the [migration documentation](https://github.com/apache/arrow/issues/14542) for further details.*}

The issue asks the Java implementation to split and transfer validity-buffer contents a word at a time instead of a byte at a time. Start by locating the validity-buffer transfer implementation and its existing tests, then verify that transfer behavior remains correct while using word-sized operations.

Written by the indexing model from the issue text.