gh-82367: Use FindFirstFile Win32 API in ntpath.realpath() (GH-110298)

* Use `FindFirstFile` Win32 API to fix a bug where `ntpath.realpath()`
breaks out of traversing a series of paths where a (handled)
`ERROR_ACCESS_DENIED` or `ERROR_SHARING_VIOLATION` occurs.
* Update docs to reflect that `ntpath.realpath()` eliminates MS-DOS
style names.

Lib/test/test_ntpath.py

@@ -2,6 +2,7 @@ import inspect
 import ntpath
 import os
 import string
+import subprocess
 import sys
 import unittest
 import warnings
@@ -637,6 +638,48 @@ class TestNtpath(NtpathTestCase):
         with os_helper.change_cwd(test_dir_short):
             self.assertPathEqual(test_file_long, ntpath.realpath("file.txt"))
 
+    @unittest.skipUnless(HAVE_GETFINALPATHNAME, 'need _getfinalpathname')
+    def test_realpath_permission(self):
+        # Test whether python can resolve the real filename of a
+        # shortened file name even if it does not have permission to access it.
+        ABSTFN = ntpath.realpath(os_helper.TESTFN)
+
+        os_helper.unlink(ABSTFN)
+        os_helper.rmtree(ABSTFN)
+        os.mkdir(ABSTFN)
+        self.addCleanup(os_helper.rmtree, ABSTFN)
+
+        test_file = ntpath.join(ABSTFN, "LongFileName123.txt")
+        test_file_short = ntpath.join(ABSTFN, "LONGFI~1.TXT")
+
+        with open(test_file, "wb") as f:
+            f.write(b"content")
+        # Automatic generation of short names may be disabled on
+        # NTFS volumes for the sake of performance.
+        # They're not supported at all on ReFS and exFAT.
+        subprocess.run(
+            # Try to set the short name manually.
+            ['fsutil.exe', 'file', 'setShortName', test_file, 'LONGFI~1.TXT'],
+            creationflags=subprocess.DETACHED_PROCESS
+        )
+
+        try:
+            self.assertPathEqual(test_file, ntpath.realpath(test_file_short))
+        except AssertionError:
+            raise unittest.SkipTest('the filesystem seems to lack support for short filenames')
+
+        # Deny the right to [S]YNCHRONIZE on the file to
+        # force nt._getfinalpathname to fail with ERROR_ACCESS_DENIED.
+        p = subprocess.run(
+            ['icacls.exe', test_file, '/deny', '*S-1-5-32-545:(S)'],
+            creationflags=subprocess.DETACHED_PROCESS
+        )
+
+        if p.returncode:
+            raise unittest.SkipTest('failed to deny access to the test file')
+
+        self.assertPathEqual(test_file, ntpath.realpath(test_file_short))
+
     def test_expandvars(self):
         with os_helper.EnvironmentVarGuard() as env:
             env.clear()