RFR: 8315149: Add hsperf counters for CPU time of internal GC threads [v17]

[Jonathan Joo]

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

Jonathan Joo has updated the pull request incrementally with one additional commit since the last revision:

  Add unit test to check existence of GC CPU counters

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Changes:
  - all: https://git.openjdk.org/jdk/pull/15082/files
  - new: https://git.openjdk.org/jdk/pull/15082/files/8b6c5533..4e51426b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15082&range=16
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15082&range=15-16

  Stats: 38 lines in 1 file changed: 38 ins; 0 del; 0 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