In the near future we'll have more cases where Ref construction is not
guaranteed to succeed. Currently, we don't have convenient patterns to
support optional construction. This CL adds the following helpers:

 base::Optional<FooRef> ref = TryMakeRef(broker, o);
 if (!ref.has_value()) return {};  // bailout
 // .. use ref.

Or, in the case where construction is guaranteed to succeed:

 FooRef ref = MakeRef(broker, o);
 // .. use ref.

Bug: v8:7790
Change-Id: I759235c314056c080d79ec413125d3957452c64c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2859169Reviewed-by: Georg Neis <neis@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74325}