[lworld] RFR: 8368799: [lworld] Heapwalking functions may report array classes several times

[Alex Menkov]

The change adds test to verify heap walking API (FollowReferences and IterateOverReachableObjects) do not reports array classes several times

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Commit messages:
 - jcheck
 - heapwalk_dup_classes
 - Merge branch 'openjdk:lworld' into lworld
 - Revert "ctor_debug"
 - ctor_debug

Changes: https://git.openjdk.org/valhalla/pull/1852/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1852&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8368799
  Stats: 226 lines in 2 files changed: 226 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/valhalla/pull/1852.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1852/head:pull/1852

PR: https://git.openjdk.org/valhalla/pull/1852