Revision of JMH Tests

This updates all perf testing to use only JMH. I tried to get all of them to follow a common pattern, and to comply with examples at https://github.com/nitsanw/jmh-samples/blob/master/src/main/java/org/openjdk/jmh/samples/ by @nitsanw. (@nitsanw if you're willing to take a look at this and confirm or correct them, I'd appreciate that).

I am doing this in 0.19 so that work on 0.20 has a common set of perf tests to use for comparison.