RFR: 8315149: Add hsperf counters for CPU time of internal GC threads [v48]

[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:

 - Fix namespace issues (2)
   
   Co-authored-by: Stefan Johansson <54407259+kstefanj at users.noreply.github.com>
 - Fix namespace issues
   
   Co-authored-by: Stefan Johansson <54407259+kstefanj at users.noreply.github.com>

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Changes:
  - all: https://git.openjdk.org/jdk/pull/15082/files
  - new: https://git.openjdk.org/jdk/pull/15082/files/fcc7e471..abb90258

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15082&range=47
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15082&range=46-47

  Stats: 6 lines in 2 files changed: 4 ins; 0 del; 2 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