RFR: 8313394: Array Elements in OldObjectSample event should be -1 if the object is not an array

[KIRIYAMA Takuya]

With this fix, arrayElements attribute in OldObjectSample event will be -1 if the object is not an array.  
Could anyone please review this fix?

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Commit messages:
 - 8313394: Array Elements in OldObjectSample event should be -1 if the object is not an array
 - 8313394: Array Elements in OldObjectSample event should be -1 if the object is not an array

Changes: https://git.openjdk.org/jdk/pull/15084/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15084&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8313394
  Stats: 108 lines in 2 files changed: 107 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/15084.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15084/head:pull/15084

PR: https://git.openjdk.org/jdk/pull/15084