Add types to private and internal properties

Author: nicolas-grekas

Filesystem.php

@@ -22,7 +22,7 @@
  */
 class Filesystem
 {
-    private static $lastError;
+    private static ?string $lastError = null;
 
     /**
      * Copies a file.

Path.php

@@ -42,12 +42,9 @@ final class Path
      *
      * @var array<string, string>
      */
-    private static $buffer = [];
+    private static array $buffer = [];
 
-    /**
-     * @var int
-     */
-    private static $bufferSize = 0;
+    private static int $bufferSize = 0;
 
     /**
      * Canonicalizes the given path.