In order to create less tasks that each need to swap permissions for
writing to the code space, merge the two {CopyAndRelocTask} and
{PublishTask} into a single {DeserializeCodeTask}.

This also makes the code a lot shorter, and removes stress from the
scheduler.

R=ahaas@chromium.org

Bug: v8:11974, chromium:1297999
Change-Id: I8866bf7225b0bc2dd4caef79e64cacca9de15519
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3468902Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79139}