fs: add fs/promises alias module

doc/api/fs.md

@@ -4237,7 +4237,7 @@ this API: [`fs.writev()`][].
 
 The `fs.promises` API provides an alternative set of asynchronous file system
 methods that return `Promise` objects rather than using callbacks. The
-API is accessible via `require('fs').promises`.
+API is accessible via `require('fs').promises` or `require('fs/promises')`.
 
 ### class: `FileHandle`
 <!-- YAML

lib/fs/promises.js

@@ -0,0 +1,3 @@
+'use strict';
+
+module.exports = require('internal/fs/promises').exports;

node.gyp

@@ -51,6 +51,7 @@
       'lib/domain.js',
       'lib/events.js',
       'lib/fs.js',
+      'lib/fs/promises.js',
       'lib/http.js',
       'lib/http2.js',
       'lib/_http_agent.js',

test/es-module/test-esm-fs-promises.mjs

@@ -0,0 +1,5 @@
+import '../common/index.mjs';
+import { stat } from 'fs/promises';
+
+// Should not reject.
+stat(new URL(import.meta.url));

test/parallel/test-fs-promises-exists.js

@@ -0,0 +1,6 @@
+'use strict';
+
+require('../common');
+const assert = require('assert');
+
+assert.strictEqual(require('fs/promises'), require('fs').promises);