Make NewCompilationJob methods return a unique_ptr to explicitly
transfer ownership.

R=mstarzinger@chromium.org

Bug: v8:9183
Change-Id: I1cc6614cc1941b1b27489443a3c330cf6e88f089
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1660474Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62206}