os,syscall: File.Stat to use file handle for directories on Windows

os,syscall: File.Stat to use file handle for directories on Windows

Updates syscall.Open to support opening directories via CreateFileW.

CreateFileW handles are more versatile than FindFirstFile handles.
They can be used in Win32 APIs like GetFileInformationByHandle and
SetFilePointerEx, which are needed by some Go APIs.

Fixes #52747
Fixes #36019

Change-Id: I26a00cef9844fb4abeeb18d2f9d854162a146651
Reviewed-on: https://go-review.googlesource.com/c/go/+/405275
Reviewed-by: Roland Shoemaker <roland@golang.org>
Reviewed-by: Patrik Nyblom <pnyb@google.com>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Run-TryBot: Quim Muntal <quimmuntal@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>