The intent of this work is to create a clean interface header file for
the snapshot component. As a first step, move SerializedData and
SnapshotData into their own dedicated files.

Bug: v8:10416
Change-Id: I95af08508555a2ec3c2364094b81a76e3e6bb38a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2144117
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67269}