RFR: 8372: Add UnitLookup.TIMESPAN to AttributeSelection to be able to use the attribute in FlameGraph for IO

[Hélios GILLES]

Add UnitLookup.TIMESPAN to AttributeSelection to be able to use the attribute in FlameGraph for IO

https://ibb.co/mrBQpYbQ

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Commit messages:
 - 8372: Add UnitLookup.TIMESPAN to AttributeSelection to be able to use the attribute in FlameGraph for IO

Changes: https://git.openjdk.org/jmc/pull/634/files
  Webrev: https://webrevs.openjdk.org/?repo=jmc&pr=634&range=00
  Issue: https://bugs.openjdk.org/browse/JMC-8372
  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jmc/pull/634.diff
  Fetch: git fetch https://git.openjdk.org/jmc.git pull/634/head:pull/634

PR: https://git.openjdk.org/jmc/pull/634