RFR: 6885: VM_OPERATION_DURATION aggregator does not filter on type

[Jean-Philippe Bempel]

Missing VM_OPERATION type to filter only on VM operations

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Commit messages:
 - fix formatting
 - Fix VM_OPERATION_DURATION aggregator

Changes: https://git.openjdk.java.net/jmc/pull/101/files
 Webrev: https://webrevs.openjdk.java.net/jmc/101/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JMC-6885
  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jmc/pull/101.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/101/head:pull/101

PR: https://git.openjdk.java.net/jmc/pull/101