Merge branch '6.1' into 6.2

* 6.1:
  [String] Fix snake conversion
  [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
  [Serializer] Fix throwing right exception in ArrayDenormalizer with invalid type

Author: derrabus

AbstractString.php

@@ -244,7 +244,7 @@ abstract public function chunk(int $length = 1): array;
     public function collapseWhitespace(): static
     {
         $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;
     }

AbstractUnicodeString.php

@@ -348,7 +348,7 @@ public function reverse(): static
 
     public function snake(): static
     {
-        $str = $this->camel()->title();
+        $str = $this->camel();
         $str->string = mb_strtolower(preg_replace(['/(\p{Lu}+)(\p{Lu}\p{Ll})/u', '/([\p{Ll}0-9])(\p{Lu})/u'], '\1_\2', $str->string), 'UTF-8');
 
         return $str;

ByteString.php

@@ -339,7 +339,7 @@ public function slice(int $start = 0, int $length = null): static
 
     public function snake(): static
     {
-        $str = $this->camel()->title();
+        $str = $this->camel();
         $str->string = strtolower(preg_replace(['/([A-Z]+)([A-Z][a-z])/', '/([a-z\d])([A-Z])/'], '\1_\2', $str->string));
 
         return $str;

Tests/AbstractAsciiTestCase.php

@@ -1041,6 +1041,7 @@ public static function provideCamel()
     {
         return [
             ['', ''],
+            ['xY', 'x_y'],
             ['symfonyIsGreat', 'symfony_is_great'],
             ['symfony5IsGreat', 'symfony_5_is_great'],
             ['symfonyIsGreat', 'Symfony is great'],
@@ -1063,6 +1064,8 @@ public static function provideSnake()
     {
         return [
             ['', ''],
+            ['x_y', 'x_y'],
+            ['x_y', 'X_Y'],
             ['symfony_is_great', 'symfonyIsGreat'],
             ['symfony5_is_great', 'symfony5IsGreat'],
             ['symfony5is_great', 'symfony5isGreat'],