This is a reland of 5c4b8056

Original change's description:
> [snapshot] Extract more files
>
> This moves:
>
> - ExternalReferenceEncoder to codegen/external-reference-encoder.h
> - SerializerDeserializer to snapshot/serializer-deserializer.h
> - Checksum() to snapshot/snapshot-utils.h
>
> serializer-common.h and .cc are removed.
>
> Tbr: clemensb@chromium.org,ulan@chromium.org
> Bug: v8:10416
> Change-Id: I36a242dcc1ad8833374aa567f73e0d4a75632c58
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2144118
> Commit-Queue: Jakob Gruber <jgruber@chromium.org>
> Reviewed-by: Jakob Gruber <jgruber@chromium.org>
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Reviewed-by: Clemens Backes <clemensb@chromium.org>
> Reviewed-by: Dan Elphick <delphick@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#67281}

Tbr: delphick@chromium.org,clemensb@chromium.org,ulan@chromium.org
Bug: v8:10416
Change-Id: I6f6a1017435db185778ed931e1ddb13d8d5e920e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2157384Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Dan Elphick <delphick@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67298}