Host info used to be stored on the global reference underlying a Ref;
now it is stored in a JSWeakMap and hence tied to the lifetime of the
actual object on V8's heap.
Additionally, the internal metadata needed for C-API functions is now
stored on the SharedFunctionInfo and no longer overlaps with the host
info mechanism.

Bonus content:
Roll 6db391e: Remove a few more leftover uses of _enum types

Change-Id: Ibb1fa4b0dd5157fef15c030bac705a11aa3beaea
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1768368Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63400}