Since StreamedSource takes ownership of the ExternalSourceStream
passed into it, it should take it by unique_ptr rather than raw
pointer to signal this transfer of ownership. The old constructor
is now deprecated.

Change-Id: I24681926c2f3141f7dd3664f72019a4c6deabfd7
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1520713
Commit-Queue: Yang Guo <yangguo@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60232}