Replace winapi with windows-sys

[Kijewski]

Some time ago I spoke in favor of using winapi instead of windows-sys, because it had fewer msrv bumps, and because it was used by e.g. tokio, and chrono, so even if it was not being developed for anymore, it still had a ton of users who would hopefully notice any bugs. By now tokio has switched to windows-sys, and chrono will too in the next release. I guess it's time then to make the switch, too.