win: fix fs.realpath.native for long paths

Unlike other fs.js functions that work with paths, realpath.native isn't
using pathModule.toNamespacedPath prior to calling libuv function. This
is causing issues on windows.

Windows long path test is also improved to cover the mentioned issue.

Fixes: #39721
PR-URL: #44536
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Gerhard Stöbich <deb2001-github@yahoo.de>

lib/fs.js

@@ -2598,7 +2598,7 @@ realpathSync.native = (path, options) => {
   options = getOptions(options);
   path = getValidatedPath(path);
   const ctx = { path };
-  const result = binding.realpath(path, options.encoding, undefined, ctx);
+  const result = binding.realpath(pathModule.toNamespacedPath(path), options.encoding, undefined, ctx);
   handleErrorFromBinding(ctx);
   return result;
 };
@@ -2758,7 +2758,7 @@ realpath.native = (path, options, callback) => {
   path = getValidatedPath(path);
   const req = new FSReqCallback();
   req.oncomplete = callback;
-  return binding.realpath(path, options.encoding, req);
+  return binding.realpath(pathModule.toNamespacedPath(path), options.encoding, req);
 };
 
 /**

test/parallel/test-fs-long-path.js

@@ -43,4 +43,7 @@ console.log({
 
 fs.writeFile(fullPath, 'ok', common.mustSucceed(() => {
   fs.stat(fullPath, common.mustSucceed());
+
+  // Tests https://github.com/nodejs/node/issues/39721
+  fs.realpath.native(fullPath, common.mustSucceed());
 }));