Add "jvm_compilation_time_total" counter (CompilationMXBean.getTotalCompilationTime)

[rainerjung]

trafficstars

The subject says it all. It is one of the few missing metrics from the standard platform MBeans.

[fstab]

Hi thanks a lot for your PRs. I saw them, and I will get back to this as soon as I found time to test this with different Java versions (IBM's J9, etc.).

[dhoard]

@rainerjung are you planning on implementing the suggestions? ... if not, I'll submit a PR based on your work and the suggestions.

[rainerjung]

@dhoard If you could pick up the ball, that would be really great! Thank you!

[dhoard]

@rainerjung new PR https://github.com/prometheus/client_java/pull/798 create.

Since getTotalCompilationTime() returns milliseconds, I chose to expose the value as is.

[dhoard]

@rainerjung please close this PR since I have picked up the work. Thanks!