RFR: 8342818: Implement CPU Time Profiling for JFR [v5]

[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 two additional commits since the last revision:

 - Tag methods and classes in the signal handler
   
   This should be valid, as the tagging only uses atomic boolean bit
   operations. This should prevent the methods and classes from
   being unloaded before they are written out by JFR.
 - Half size of JfrAsyncStackFrame
   
   Encode line=-1 in the type and remove the Klass pointer,
   reducing the size of the JfrAsyncStackFrame class from
   32 to 16 bytes. Effectively halving the memory required
   for the queue.

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/20752/files
  - new: https://git.openjdk.org/jdk/pull/20752/files/ddec72bc..1e0dbaea

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20752&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20752&range=03-04

  Stats: 38 lines in 2 files changed: 25 ins; 2 del; 11 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