RFR: 8296229: JFR: jfr tool should print unsigned values correctly

[Erik Gahlin]

Could I have a review of PR that fixes so unsigned numbers are printed correctly in the jfr tool.

Testing:
test/jdk/jdk/jfr
test/jdk/jdk/security/logging/

Thanks
Erik

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Commit messages:
 - Initial

Changes: https://git.openjdk.org/jdk/pull/11039/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11039&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8296229
  Stats: 78 lines in 15 files changed: 36 ins; 1 del; 41 mod
  Patch: https://git.openjdk.org/jdk/pull/11039.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11039/head:pull/11039

PR: https://git.openjdk.org/jdk/pull/11039