RFR: 8291753: Add JFR event for GC CPU Time

[Sangheon Kim]

Hi all,

Could I have reviews to add new JFR event for GC CPU time?
Currently only log message is available for CPU time (user, system, real).
As there is already GCTraceCPUTime class which is used for a log message, I added GCTracer to deliver the event.
The log message of CPU time is printed after GC is completed and tried to keep same.

For G1, manually checked there is not difference.

For test, I had to add an exception as GCCpuTime will be generated after GC end.

Testing: tier 1 ~ 3

Thanks,
Sangheon

-------------

Commit messages:
 - Split G1FullGCMark
 - Add JFR event of GCCpuTime.

Changes: https://git.openjdk.org/jdk/pull/9760/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9760&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8291753
  Stats: 181 lines in 20 files changed: 136 ins; 11 del; 34 mod
  Patch: https://git.openjdk.org/jdk/pull/9760.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9760/head:pull/9760

PR: https://git.openjdk.org/jdk/pull/9760