[jdk22] RFR: 8323159: Consider adding some text re. memory zeroing in Arena::allocate

[Per Minborg]

8323159: Consider adding some text re. memory zeroing in Arena::allocate

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Commit messages:
 - Backport f5b757ced6b672010ea10575d644d3f9d1728923

Changes: https://git.openjdk.org/jdk22/pull/77/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk22&pr=77&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8323159
  Stats: 51 lines in 2 files changed: 49 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk22/pull/77.diff
  Fetch: git fetch https://git.openjdk.org/jdk22.git pull/77/head:pull/77

PR: https://git.openjdk.org/jdk22/pull/77