Refactor-only: This moves declaration of implementation details into
the .cc file. No logic changes.

Bug: v8:9574
Change-Id: I985ce17138e65f18dbb629b9f6660009e034fbf0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1786279
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Maya Lekova <mslekova@chromium.org>
Auto-Submit: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63562}