RFR: 8326116: JFR: Add help option to -XX:StartFlightRecording

[Erik Gahlin]

Could I have review of an enhancement that adds a help option to -XX:StartFlightRecording similar to -Xlog:help.

Testing: jdk/jdk/jfr + tier1 + tier2

Thanks
Erik

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Commit messages:
 - Initial

Changes: https://git.openjdk.org/jdk/pull/18765/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18765&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8326116
  Stats: 129 lines in 5 files changed: 106 ins; 0 del; 23 mod
  Patch: https://git.openjdk.org/jdk/pull/18765.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18765/head:pull/18765

PR: https://git.openjdk.org/jdk/pull/18765