Re: GetNamedLWLockTranche crashes on Windows in normal backend

commit 38b602b certainly doesn't do us any favors here since it
> removed NamedLWLockTrancheArray.  Given the lack of reports from the field,
> I suspect the best path forward is to add an ERROR for unsafe accesses and
> to fix the documentation, as discussed upthread.

I suggest we set an in progres flag for shmem_startup_hook, as we do for
shmem_request_hook, and error out this function if called outside of this
hook. The error will be something like this:

```
ERROR:  cannot return the address of LWLocks outside of shmem_startup_hook
```

We can also update the docs.

If you agree with the above, I'll get the patch ready?

--
Sami Imseih
Amazon Web Services (AWS)