RFR: 8345339: JFR: Missing javadoc for RecordingStream::onMetadata

[Erik Gahlin]

Could I have a review of a change that adds missing javadoc for the RecordingStream::onMetadata.

Testing: tier1 + test/jdk/jdk/jfr

Thanks
Erik

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Commit messages:
 - Initial

Changes: https://git.openjdk.org/jdk/pull/22547/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22547&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8345339
  Stats: 42 lines in 2 files changed: 42 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/22547.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22547/head:pull/22547

PR: https://git.openjdk.org/jdk/pull/22547