Profiler samples for native time too

[sandybrownlee]

Currently the profiler looks for JFR jdk.ExecutionSample events. These are Java code running. We should also be counting jdk.NativeMethodSample events - which are when native code is running. These include blocked threads like I/O waits, so we'd need to do this:

String state = e.getString("state"); // e.g., "RUNNABLE", "SLEEPING", ...
      if ("RUNNABLE".equals(state)) nativeOnCpu++;

to filter the counts of native events to only when the code is running. This should improve the accuracy of profiling.