Merge branch '4.4' into 5.4

* 4.4:
  [DowCrawler] Fix locale-sensitivity of whitespace normalization
  suggest to install the Twig bundle when the required component is already installed
  Update PULL_REQUEST_TEMPLATE.md

Author: nicolas-grekas

AbstractString.php

@@ -245,7 +245,7 @@ abstract public function chunk(int $length = 1): array;
     public function collapseWhitespace(): self
     {
         $str = clone $this;
-        $str->string = trim(preg_replace('/(?:\s{2,}+|[^\S ])/', ' ', $str->string));
+        $str->string = trim(preg_replace("/(?:[ \n\r\t\x0C]{2,}+|[\n\r\t\x0C])/", ' ', $str->string), " \n\r\t\x0C");
 
         return $str;
     }