[jdk18u] RFR: 8281318: Improve jfr/event/allocation tests reliability [v2]

[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

Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

 - Merge branch 'master' into JDK-8281318-jfr-32bit
 - Backport 65831eb294b6f1f5f99988836c00005d41c27fd3

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk18u/pull/42/files
  - new: https://git.openjdk.java.net/jdk18u/pull/42/files/9d8bda7f..dd8d894b

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk18u&pr=42&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk18u&pr=42&range=00-01

  Stats: 257 lines in 9 files changed: 227 ins; 5 del; 25 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