Fix #11583. Changed os.path.isdir to use GetFileAttributes instead of os.stat.

By changing to the Windows GetFileAttributes API in nt._isdir we can figure
out if the path is a directory without opening the file via os.stat. This has
the minor benefit of speeding up os.path.isdir by at least 2x for regular
files and 10-15x improvements were seen on symbolic links (which opened the
file multiple times during os.stat). Since os.path.isdir is used in
several places on interpreter startup, we get a minor speedup in startup time.
diff --git a/Misc/NEWS b/Misc/NEWS
index 16a0f29..15ed46f 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -22,6 +22,9 @@
 Library
 -------
 
+- Issue #11583: Speed up os.path.isdir on Windows by using GetFileAttributes
+  instead of os.stat.
+
 - Named tuples now work correctly with vars().
 
 - Issue #12085: Fix an attribute error in subprocess.Popen destructor if the