RFR: Implement JEP 509: JFR CPU-Time Profiling [v44]

[Johannes Bechberger]

> This is the code for the [JEP draft: CPU Time based profiling for JFR].
> 
> Currently tested using [this test suite](https://github.com/parttimenerd/basic-profiler-tests).
> 
> A version based on the cooperative sampling JEP can be found [here](https://github.com/parttimenerd/jdk/tree/parttimenerd_cooperative_cpu_time_sampler).

Johannes Bechberger has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains one commit:

  Implement CPU time sampler that emits events at safepoints
  
  The stacktraces are recorded in the signal handler,
  but the JFR events are only created at safepoints
  (except when a thread is in native too long).

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Changes: https://git.openjdk.org/jdk/pull/20752/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20752&range=43
  Stats: 2667 lines in 53 files changed: 2492 ins; 147 del; 28 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