Stat uses Windows FindFirstFile + CreateFile to gather symlink
information - FindFirstFile determines if file is a symlink,
and then CreateFile follows symlink to capture target details.

Lstat only uses FindFirstFile.

This CL replaces current approach with just a call to CreateFile.
Lstat uses FILE_FLAG_OPEN_REPARSE_POINT flag, that instructs
CreateFile not to follow symlink. Other than that both Stat and
Lstat look the same now. New code is simpler.

CreateFile + GetFileInformationByHandle (unlike FindFirstFile)
does not report reparse tag of a file. I tried to ignore reparse
tag altogether. And it works for symlinks and mount points.
Unfortunately (see https://github.com/moby/moby/issues/37026),
files on deduped disk volumes are reported with
FILE_ATTRIBUTE_REPARSE_POINT attribute set and reparse tag set
to IO_REPARSE_TAG_DEDUP. So, if we ignore reparse tag, Lstat
interprets deduped volume files as symlinks. That is incorrect.
So I had to add GetFileInformationByHandleEx call to gather
reparse tag after calling CreateFile and GetFileInformationByHandle.

Fixes #27225
Fixes #27515

Change-Id: If60233bcf18836c147597cc17450d82f3f88c623
Reviewed-on: https://go-review.googlesource.com/c/143578
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Kirill Kolyshkin <kolyshkin@gmail.com>