RFR: 8321300: Cleanup TestHFA

[Martin Doerr]

I'd like to clean this up: Use the canonical layouts which are available in JDK22. Use try-with-resources for `Arena.ofConfined()`.

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Commit messages:
 - 8321300: Cleanup TestHFA

Changes: https://git.openjdk.org/jdk/pull/16959/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16959&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8321300
  Stats: 141 lines in 1 file changed: 1 ins; 10 del; 130 mod
  Patch: https://git.openjdk.org/jdk/pull/16959.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16959/head:pull/16959

PR: https://git.openjdk.org/jdk/pull/16959