Release Note: New PerfCounters for STW Phases on Concurrent GC Are Available

A new GC performance counter has been added for pauses during the concurrent phase. This counter will be listed by `jstat` under the CGC (concurrent GC) heading. This information is only available for GCs with a concurrent phase and is GC specific:
* G1 includes remark and cleanup pauses
* CMS includes initial mark and remark pauses

For CMS, these pauses were previously included in the time listed by `jstat` under the FGC (full GC) heading.

The information is also available via the `jcmd` by using `PerfCounter.print`.