Add an {ObjectRef} class to Handle which is returned by {operator->}.
Before, it returned {T} directly, and then used {T::operator->} for
the chained {operator->}.
As a drive-by, this CL also removes {HandleBase::operator*} and
implements this in {Handle<T>} directly.

R=jkummerow@chromium.org

Bug: v8:9183, v8:3770
Change-Id: I0a79fbbc393539543a62773c98a39c7bc2a84b77
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1624206Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61734}