.. by turning `masm_` into a unique_ptr s.t. it's freed after the
NoRootArrayScope which references it.

Fixed: chromium:1252620
Change-Id: I24580c5a96d76a973b2b083e7a76b95f93bb6068
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3185459
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Patrick Thier <pthier@chromium.org>
Auto-Submit: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Patrick Thier <pthier@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77082}