Organize Windows build

[ericmehl]

The main requirement here is to put all binaries a Python .pyd module requires is in the same directory, or otherwise available based on Python 3.8's new DLL search method : https://docs.python.org/3/whatsnew/3.8.html#bpo-36085-whatsnew

Most notably, PATH is no longer part of the search path for module dependencies.

I think it's also worth doing a few other cleanups :

• Put all .dll files in bin. Right now they're scattered between bin, lib and probably some other places.
• Put all .lib files in lib, and only .lib files. .lib files on Windows are required for linking to a .dll, so they are developer-facing rather than user-facing. Right now a number of .dll files live in lib as well, and I think those are better off in bin.
• There are some weird placements of Python modules generated by dependencies - site-packages, python and some others are used inconsistently. Maybe not the biggest problem if things are working, but it might be nice to keep it tidy.

Any other improvements are welcome!

[ericmehl]

This is done on branch 9_maintenance_vs2022 with the exception of the "only .lib files" in lib directory. I don't think we need to be quite that strict and some packages might even require non-lib things in lib, Python being a top guess (though I haven't tried moving those things around).