RFR: 8342818: Implement CPU Time Profiling for JFR [v2]

[Johannes Bechberger]

> This is the code for the [JEP draft: CPU Time based profiling for JFR].

Johannes Bechberger has updated the pull request incrementally with one additional commit since the last revision:

  Improve TestLookForUntestedEvents and TimespanRate.of

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Changes:
  - all: https://git.openjdk.org/jdk/pull/20752/files
  - new: https://git.openjdk.org/jdk/pull/20752/files/366aced5..9bfceee0

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20752&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20752&range=00-01

  Stats: 20 lines in 6 files changed: 8 ins; 0 del; 12 mod
  Patch: https://git.openjdk.org/jdk/pull/20752.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20752/head:pull/20752

PR: https://git.openjdk.org/jdk/pull/20752