This includes adding what should be a relatively temporary
`Modules/_decimal/windows/mpdecimal.h` shim to choose between `mpdecimal32vc.h`
or `mpdecimal64vc.h` based on which of `CONFIG_64` or `CONFIG_32` is defined.
* Add missing header files to pythoncore.
* Add missing file filters ("Resource Files" in particular) to
all projects.
* Add new sub-filters for private headers in pythoncore and
for 3rd party source files.
* Add missing _zoneinfo configurations in pcbuild.sln.
* Update bdist_wininst with the new zlib location.