RFR: 8351064: JFR: Consistent timestamps

[Erik Gahlin]

Could I have review of a PR that makes time conversion uses offsets taken from the first chunk even if user-defined events are registered and parsers are reconstructed.

Testing: jdk/jdk/jfr

Thanks
Erik

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Commit messages:
 - Initial

Changes: https://git.openjdk.org/jdk/pull/23870/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23870&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8351064
  Stats: 5 lines in 1 file changed: 4 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/23870.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23870/head:pull/23870

PR: https://git.openjdk.org/jdk/pull/23870