RFR: 8315149: Add hsperf counters for CPU time of internal GC threads [v36]

[Jonathan Joo]

> 8315149: Add hsperf counters for CPU time of internal GC threads

Jonathan Joo has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 36 additional commits since the last revision:

 - Merge branch 'openjdk:master' into master
 - Replace NULL with nullptr
 - Implement hsperf counter for G1ServiceThread
 - Remove StringDedup from GC thread list
 - Use 64-bit atomic add for incrementing counters
 - Merge branch 'openjdk:master' into master
 - Add call to publish in parallel gc and update counter names
 - Add Copyright header to test and formatting changes
 - Fix test
 - add comment and change if defined to ifdef
 - ... and 26 more: https://git.openjdk.org/jdk/compare/d748dccb...2446149c

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Changes:
  - all: https://git.openjdk.org/jdk/pull/15082/files
  - new: https://git.openjdk.org/jdk/pull/15082/files/be104e16..2446149c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15082&range=35
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15082&range=34-35

  Stats: 27809 lines in 1182 files changed: 15264 ins; 4162 del; 8383 mod
  Patch: https://git.openjdk.org/jdk/pull/15082.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15082/head:pull/15082

PR: https://git.openjdk.org/jdk/pull/15082