This allows streamed sources to also trigger parallel compile tasks. The
chunk vectors are shared via std::shared_ptr.

Clone chunked streams are initialised with a null source, and are not
allowed to fetch any more data. Similarly, the original stream is not
allowed to fetch data if it has been cloned (since the vector is shared
and would mutate if we added more data to it).

This is ok for the purposes of cloning for parallel compile tasks, as we
fully parse before cloning for the task.

Change-Id: Ic268e4956e0894acb63111bf0aaf32eaad426066
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3310917
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78209}