When a process exits cleanly, i.e. because the event loop ends up
without things to wait for, the Node.js objects that are left on
the heap should be:

 1. weak, i.e. ready for garbage collection once no longer
    referenced, or
 2. detached, i.e. scheduled for destruction once no longer
    referenced, or
 3. an unrefed libuv handle, i.e. does not keep the event loop
    alive, or
 4. an inactive libuv handle (essentially the same here)

There are a few exceptions to this rule, but generally,
if there are C++-backed Node.js objects on the heap
that do not fall into the above categories, we may be looking
at a potential memory leak. Most likely, the cause is a missing
`MakeWeak()` call on the corresponding object.

In order to avoid this kind of problem, we check the list
of BaseObjects for these criteria. In this commit, we only do so
when explicitly instructed to or when in debug mode
(where --verify-base-objects is always-on).

In particular, this avoids the kinds of memory leak issues
that were fixed in the PRs referenced below.

Refs: nodejs#35488
Refs: nodejs#35487
Refs: nodejs#35481