RFR: 8321300: Cleanup TestHFA

[Johannes Bechberger]

On Mon, 4 Dec 2023 21:25:41 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

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

Marked as reviewed by jbechberger (Committer).

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PR Review: https://git.openjdk.org/jdk/pull/16959#pullrequestreview-1764635012