This is a reland of 35a6eeec

Reland fixes:
  * Add a SharedFunctionInfo::CopyFrom to encapsulate updating the SFI
    from the placeholder. This now includes copying scope_info (which
    wasn't included in the original CL and caused some of the issues)
  * Make sure that LocalHandleScope is initialised only inside of
    UnparkedScope (fixed TSAN issues)
  * Clean-up: Don't add `script_` to ParseInfo, but instead pass it
    separately to Parser. Eventually we'd ideally get rid of ParseInfo
    entirely (splitting it into input and output) so let's not add more
    fields to it. Reverts changing CreateScript to InitializeScript.

Original change's description:
> [off-thread] Allow off-thread top-level IIFE finalization
>
> Allow off-thread finalization for parallel compile tasks (i.e. for top-
> level IIFEs).
>
> This allows us to merge the code paths in BackgroundCompileTask, and
> re-enable the compiler dispatcher tests under the off-thread
> finalization flag. Indeed, we can simplify further and get rid of that
> flag entirely (it has been on-by-default for several releases now).
>
> Change-Id: I54f361997d651667fa813ec09790a6aab4d26774
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3226780
> Reviewed-by: Toon Verwaest <verwaest@chromium.org>
> Commit-Queue: Leszek Swirski <leszeks@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#77615}

Change-Id: If1a5b14900aa6753561e34e972a293be0be9a07d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3256692
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77676}