doc: add File modes cross-references in fs methods

Adds links to the File modes section from fsPromises.open(),
fsPromises.mkdir(), and fs.mkdir() to improve discoverability
of file permission documentation.

PR-URL: #60286
Reviewed-By: Ulises Gascón <ulisesgascongonzalez@gmail.com>

Author: Mohit-Raj-Saxena

doc/api/fs.md

@@ -1221,7 +1221,8 @@ added: v10.0.0
 * `path` {string|Buffer|URL}
 * `options` {Object|integer}
   * `recursive` {boolean} **Default:** `false`
-  * `mode` {string|integer} Not supported on Windows. **Default:** `0o777`.
+  * `mode` {string|integer} Not supported on Windows. See [File modes][]
+    for more details. **Default:** `0o777`.
 * Returns: {Promise} Upon success, fulfills with `undefined` if `recursive`
   is `false`, or the first directory path created if `recursive` is `true`.
 
@@ -1325,7 +1326,8 @@ changes:
 * `flags` {string|number} See [support of file system `flags`][].
   **Default:** `'r'`.
 * `mode` {string|integer} Sets the file mode (permission and sticky bits)
-  if the file is created. **Default:** `0o666` (readable and writable)
+  if the file is created. See [File modes][] for more details.
+  **Default:** `0o666` (readable and writable)
 * Returns: {Promise} Fulfills with a {FileHandle} object.
 
 Opens a {FileHandle}.
@@ -3408,7 +3410,8 @@ changes:
 * `path` {string|Buffer|URL}
 * `options` {Object|integer}
   * `recursive` {boolean} **Default:** `false`
-  * `mode` {string|integer} Not supported on Windows. **Default:** `0o777`.
+  * `mode` {string|integer} Not supported on Windows. See [File modes][]
+    for more details. **Default:** `0o777`.
 * `callback` {Function}
   * `err` {Error}
   * `path` {string|undefined} Present only if a directory is created with
@@ -8449,6 +8452,7 @@ the file contents.
 [Common System Errors]: errors.md#common-system-errors
 [FS constants]: #fs-constants
 [File access constants]: #file-access-constants
+[File modes]: #file-modes
 [MDN-Date]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date
 [MDN-Number]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type
 [MSDN-Rel-Path]: https://docs.microsoft.com/en-us/windows/desktop/FileIO/naming-a-file#fully-qualified-vs-relative-paths