RFR: 8335730: JFR: Clean up jdk.jfr

[Erik Gahlin]

Could I have review of a PR that:
- remove unused imports
- remove unused variables in instanceof
- use constants instead Integer.valueOf(-1) or Long.valueOf(0L)
- add final where missing
- prefer package protected classes over public
- use try-with-resources
- use Arrays.toString(...) instead of Arrays.asList(...).toString();

Testing: jdk/jdk/jfr

Thanks
Erik

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Commit messages:
 - Initial

Changes: https://git.openjdk.org/jdk/pull/20042/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20042&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8335730
  Stats: 58 lines in 24 files changed: 3 ins; 22 del; 33 mod
  Patch: https://git.openjdk.org/jdk/pull/20042.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20042/head:pull/20042

PR: https://git.openjdk.org/jdk/pull/20042