[jdk17u-dev] RFR: 8297154: Improve safepoint cleanup logging

[Aleksey Shipilev]

Clean backport to improve safepoint cleanup logging.

Additional testing:
 - [x] Eyeballing `-Xlog:safepoint` logs

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Commit messages:
 - Backport 086763a629fe8b0592f5566c6e346716868d5e63

Changes: https://git.openjdk.org/jdk17u-dev/pull/1378/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=1378&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8297154
  Stats: 11 lines in 2 files changed: 9 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/1378.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/1378/head:pull/1378

PR: https://git.openjdk.org/jdk17u-dev/pull/1378