[Java][Doc] Add JavaDoc to TransferPair interface

The TransferPair interface is important to the Java vector module's memory management, but there is only a single line class comment, and no comments for the methods. The implementations of those methods have subtitles that are hidden in the method names. For example, the method transferTo() clears the memory in the original vector and resets the rowCount to 0, but splitAndTransferTo() only copies the values into new memory and the original is unchanged.  

**Reporter**: [Larry White](https://issues.apache.org/jira/browse/ARROW-17570) / @lwhite1

_{**Note**: *This issue was originally created as [ARROW-17570](https://issues.apache.org/jira/browse/ARROW-17570). Please see the [migration documentation](https://github.com/apache/arrow/issues/14542) for further details.*}

Locate the Java vector module's TransferPair interface and read its method declarations alongside their implementations. Add JavaDoc describing the distinct memory and row-count behavior of transferTo() and splitAndTransferTo(), and ensure all interface methods are documented.

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