add a ValidationLogging mix-in

inspired by / reusing some of HTSJDK's [ValidationStringency enum](https://github.com/samtools/htsjdk/blob/master/src/java/htsjdk/samtools/ValidationStringency.java) and [associated logging utilities](https://github.com/samtools/htsjdk/blob/a30bc12df2aeb3b4312a9c236c6a639025d5b596/src/java/htsjdk/samtools/SAMLineParser.java#L423).

I was going to use this in another feature but then didn't need it; happy to submit it or scrap it.