[jdk18u] RFR: 8281318: Improve jfr/event/allocation tests reliability

[Aleksey Shipilev]

Clean backport to improve JFR tests on x86_32.
Needs [JDK-8281638](https://bugs.openjdk.java.net/browse/JDK-8281638) as the follow-up.

Additional testing:
 - [x] Linux x86_32 fastdebug, affected tests fail without the patch, pass with it

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Commit messages:
 - Backport 65831eb294b6f1f5f99988836c00005d41c27fd3

Changes: https://git.openjdk.java.net/jdk18u/pull/42/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk18u&pr=42&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8281318
  Stats: 54 lines in 3 files changed: 33 ins; 0 del; 21 mod
  Patch: https://git.openjdk.java.net/jdk18u/pull/42.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk18u pull/42/head:pull/42

PR: https://git.openjdk.java.net/jdk18u/pull/42