RFR: 8339197: GenShen: Adding Generation and Evacuation Information JFR Logging

[Satyen Subramaniam]

Adding `ShenandoahEvacInfo` event and modifying existing logging for Concurrent Reset and Final Roots events to include generation for Generational Shenandoah GC.

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Commit messages:
 - Removing trailing whitespace
 - Removing comment
 - Merge branch 'openjdk:master' into JDK-8339197
 - Adding ShenandoahEvacInfo JFR Event
 - Adding gen event messages

Changes: https://git.openjdk.org/shenandoah/pull/489/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah&pr=489&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8339197
  Stats: 241 lines in 8 files changed: 234 ins; 5 del; 2 mod
  Patch: https://git.openjdk.org/shenandoah/pull/489.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/489/head:pull/489

PR: https://git.openjdk.org/shenandoah/pull/489