[sh/jdk8u] RFR 8221507: Implement JFR Events for Shenandoah

[Zhengyu Gu]

Hi,

Please review this 8u backport of JFR events for Shenandoah.

The original patch does not apply cleanly.

1) The patch has to be split into hotspot and jdk parts.
2) Adjusted @library and removed @requires vm.hasJFR tag(not supported 
in 8u) for tests
3) Removed INCLUDE_SHENANDOAHGC, sh/8u always builds with Shenandoah on.
4) Adjusted imports
5) ShenandoahHeapRegion::region_number() -> ShenandoahHeapRegion::index()
6) Manually fixed some merge conflicts


The original webrev: http://hg.openjdk.java.net/jdk/jdk/rev/43340a79840d

sh/8u webrev:
   hotspot: 
http://cr.openjdk.java.net/~zgu/shenandoah/JDK-8221507-8u/hotspot/webrev.00/
   jdk: 
http://cr.openjdk.java.net/~zgu/shenandoah/JDK-8221507-8u/jdk/webrev.00/

Test:
   Passed new tests in patch on Linux x86_64

Thanks,

-Zhengyu