RFR: 8315149: Add hsperf counters for CPU time of internal GC threads [v29]

[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 Copyright header to test and formatting changes

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Changes:
  - all: https://git.openjdk.org/jdk/pull/15082/files
  - new: https://git.openjdk.org/jdk/pull/15082/files/1e8c1a4e..fc5cf3d8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15082&range=28
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15082&range=27-28

  Stats: 28 lines in 2 files changed: 24 ins; 1 del; 3 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