This is a partial reland of https://crrev.com/c/v8/v8/+/2601880 .

This change improves readability and helps prepare for when ScopeInfo
will not be convertible to FixedArrayBase.

Change-Id: I8de453c2b72ced51e98161e3d9e6426cd6ff7267
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2707250Reviewed-by: Mythri Alle <mythria@chromium.org>
Commit-Queue: Seth Brenith <seth.brenith@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#72920}