port to Java to avoid having to maintain support for multiple scala versions

[pjfanning]

I'm just logging this for reference. Apache Drill uses this lib but it is a little out of date.

• some fixes to the Spark code are missing from here (https://github.com/apache/spark/blob/master/core/src/main/scala/org/apache/spark/util/SizeEstimator.scala)
• Scala 2.12/2.13/3.x are all released since the last release of this lib

I have a Java port of the code in a PR for Apache Drill if anyone is interested in copying the code for their own use.

https://github.com/apache/drill/pull/2665