RFR: 8331896: JFR: Improve check for JDK classes

[Erik Gahlin]

Could I have a review of change that prepares for support for JDK events in other modules besides java.base.

Testing: jdk/jdk/jfr

Thanks
Erik

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Commit messages:
 - Remove tab
 - Initial

Changes: https://git.openjdk.org/jdk/pull/19542/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19542&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8331896
  Stats: 26 lines in 6 files changed: 13 ins; 0 del; 13 mod
  Patch: https://git.openjdk.org/jdk/pull/19542.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19542/head:pull/19542

PR: https://git.openjdk.org/jdk/pull/19542