[jdk17u] RFR: 8274560: JFR: Add test for OldObjectSample event when using Shenandoah

[Aleksey Shipilev]

Clean backport to improve Shenandoah testing.

Additional testing:
 - [x] Linux x86_64 fastdebug `jdk/jfr/event/oldobject` passes

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Commit messages:
 - Backport ef0922e88528bdf4fe75537ddf4e82123e3f58b3

Changes: https://git.openjdk.java.net/jdk17u/pull/255/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk17u&pr=255&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8274560
  Stats: 80 lines in 2 files changed: 79 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk17u/pull/255.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk17u pull/255/head:pull/255

PR: https://git.openjdk.java.net/jdk17u/pull/255