windows: add WSADuplicateSocket

WSADuplicateSocket is useful to pass sockets between processes on
Windows.

For golang/go#10350.

Change-Id: I6563184fe4d4477d402a6af81b254bd8aa992d2e
Reviewed-on: https://go-review.googlesource.com/c/sys/+/668215
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Carlos Amedee <carlos@golang.org>