minor #32786 add parameter type declarations to private methods (xabbuh)

This PR was merged into the 4.4 branch.

Discussion
----------

add parameter type declarations to private methods

| Q             | A
| ------------- | ---
| Branch?       | 4.4
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets |
| License       | MIT
| Doc PR        |

Commits
-------

1b2aaa4a06 add parameter type declarations to private methods

Author: fabpot

Filesystem.php

@@ -294,13 +294,11 @@ public function rename($origin, $target, $overwrite = false)
     /**
      * Tells whether a file exists and is readable.
      *
-     * @param string $filename Path to the file
-     *
      * @return bool
      *
      * @throws IOException When windows path is longer than 258 characters
      */
-    private function isReadable($filename)
+    private function isReadable(string $filename)
     {
         $maxPathLength = PHP_MAXPATHLEN - 2;
 
@@ -381,11 +379,9 @@ public function hardlink($originFile, $targetFiles)
     }
 
     /**
-     * @param string $origin
-     * @param string $target
      * @param string $linkType Name of the link type, typically 'symbolic' or 'hard'
      */
-    private function linkException($origin, $target, $linkType)
+    private function linkException(string $origin, string $target, string $linkType)
     {
         if (self::$lastError) {
             if ('\\' === \DIRECTORY_SEPARATOR && false !== strpos(self::$lastError, 'error code(1314)')) {