help me improve behavior on Windows?

Hi friends,

In 7.66.0 we merged code into curl that makes it provide a socket for
applications to wait for during the threaded name resolve phase, removing the
need for polling for status and thus figuring out how often to poll or even in
some cases end up busy-looping like crazy.

That change was done using socketpair() and therefor it unfortunately only
works on linux and unix-like systems.

To bring that same improvement and benefit to the Windows side of libcurl,
I've written a custom socketpair() implementation for Windows that can be used
on that platform to offer the same functionality.

I've written it based on documentation, google searches and repeated CI runs.
** I have not used it myself on Windows! **

This is where I hope for some help and assistance: I would like some review
and help with testing this patch out on Windows, ideally with a real-world
application, for a little bit to verify that it doesn't totally crash and
burn.

This work can be found in PR #4466 on github:

   https://github.com/curl/curl/pull/4466

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