Make off-thread deserialization play well with the Isolate compilation
cache, by moving the Finish call into GetSharedFunctionInfoForScript.

This means that

  a) The isolate cache is checked before the Finish, allowing it to be
     hit, and
  b) Results of off-thread deserializations are written into the Isolate
     cache.

Bug: chromium:1075999
Change-Id: I535935180bbe77f3e718253830e649bd62857634
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3094006
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#76341}