RFR (M): 8209061: Move G1 serviceability functionality to G1MonitoringSupport

[Thomas Schatzl]

Hi all,

  can I have reviews for this cleanup that moves all serviceability
functionality into the G1MonitoringSupport class.

CR:
https://bugs.openjdk.java.net/browse/JDK-8209061
Webrev:
http://cr.openjdk.java.net/~tschatzl/8209061/webrev/
Testing:
hs-tier1-4, jdk-tier1-3

Depends on JDK-8208498 also out for review.

Thanks,
  Thomas