[String] Allow to define slugger substitutions with PHP closures

Author: javiereguiluz

components/string.rst

@@ -473,10 +473,19 @@ that only includes safe ASCII characters::
     $slug = $slugger->slug('10% or 5€');
     // $slug = '10-percent-or-5-euro'
 
+    // for more dynamic substitutions, pass a PHP closure instead of an array
+    $slugger = new AsciiSlugger('en', function ($string, $locale) {
+        return str_replace('❤️', 'love', $string);
+    });
+
 .. versionadded:: 5.1
 
     The feature to define additional substitutions was introduced in Symfony 5.1.
 
+.. versionadded:: 5.2
+
+    The feature to use a PHP closure to define substitutions was introduced in Symfony 5.2.
+
 The separator between words is a dash (``-``) by default, but you can define
 another separator as the second argument::