RFR: 8315149: Add hsperf counters for CPU time of internal GC threads [v37]

[Jonathan Joo]

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

Jonathan Joo has updated the pull request incrementally with two additional commits since the last revision:

 - revert gitignore change
 - Attempt to fix broken test

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Changes:
  - all: https://git.openjdk.org/jdk/pull/15082/files
  - new: https://git.openjdk.org/jdk/pull/15082/files/2446149c..9fb36a9e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15082&range=36
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15082&range=35-36

  Stats: 3 lines in 1 file changed: 3 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