This is the 2nd step in series of CLs to move the SharedFunctionInfo
class to kNeverSerialized and make it concurrently accessible from
the background thread. This CL:
* Changes optimization of GetTemplateObject in JSCreateLowering to
  only perform the optimization of a template object exists in the
  SharedFunctionInfo[Ref], but skips the optimization if one is
  missing instead of allocating a new one on demand.

Bug: v8:7790
Change-Id: Ic37d8333676e54b3f8d69416480df12bd90723ea
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2463229
Commit-Queue: Nico Hartmann <nicohartmann@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Reviewed-by: Santiago Aboy Solanes <solanes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71189}