RFR: 8298383: JFR: GenerateJfrFiles.java lacks copyright header

[Erik Gahlin]

Could I have a review of PR that adds missing copyright header to GenerateJfrFiles.java

Testing: tier1 

Thanks
Erik

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Commit messages:
 - Initial

Changes: https://git.openjdk.org/jdk/pull/11591/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11591&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8298383
  Stats: 25 lines in 1 file changed: 25 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/11591.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11591/head:pull/11591

PR: https://git.openjdk.org/jdk/pull/11591