We currently have a pattern of setting a dereferenced Handle location to
update that Handle's value:

  *handle.location() = new_value.ptr()

This is slightly opaque, and definitely not type-safe, so add a new
Handle<T>::PatchValue method which does this operation.

Ideally we would make Handle::location() return a const pointer to
discourage this sort of use, but there's a bunch of places where that
location pointer is used and passed around as a Handle surrogate, so
those would have to be updated first.

Change-Id: I157f7e2473ed1b86f7a93cae260b0932fed0ad88
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2424249
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70088}