Introduce a helper class for regular expression parsing
and use it to improve load poison tests readability and
maintainability.

Extend load poisoning tests for arm64 platform (e.g.
for both regular and compressed references cases).

Change-Id: Ie62dfd14a60186feaa5f48e1a6122d77766472af
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1645913
Commit-Queue: Martyn Capewell <martyn.capewell@arm.com>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62493}