RFR: 8338314: JFR: Split JFRCheckpoint VM operation

[Aleksey Shipilev]

Investigating JFR crashes is a bit tedious, as Events section in `hs_err` shows just:


Event: 3.006 Executing VM operation: JFRCheckpoint
Event: 3.006 Executing VM operation: JFRCheckpoint done


What is that `JFRCheckpoint` doing is unclear, because it can do two separate things: clear or write. It would be good if we could disambiguate the two. Since there are only two flavors of checkpoint, I think we can just split the VMOp into two more precisely named ones, so it gives us e.g.:


Event: 2.462 Executing VM operation: JFRSafepointClear
Event: 2.463 Executing VM operation: JFRSafepointClear done

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Commit messages:
 - Fix

Changes: https://git.openjdk.org/jdk/pull/20570/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20570&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8338314
  Stats: 23 lines in 3 files changed: 12 ins; 1 del; 10 mod
  Patch: https://git.openjdk.org/jdk/pull/20570.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20570/head:pull/20570

PR: https://git.openjdk.org/jdk/pull/20570