[extensions] Update several tests to use MakeRefCounted instead of new

A lot of usage of ExtensionFunctions in tests create scoped_refpts using
bare new calls, but we prefer using MakeRefCounted in these cases.

This CL updates a collection of such tests to do so and normalizes the
type used to 'auto' where appropriate. No behavior change is expected.

Bug: 1384857
Change-Id: I94ecea6f97b48c1e20fc6a35a277c343eb69fc3d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4023972


Reviewed-by: David Bertoni <dbertoni@chromium.org>
Commit-Queue: Tim <tjudkins@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1072309}