Merge branch '4.4'

* 4.4:
  [Debug] Improve UPGRADE files
  remove wrongly added legacy group from test
  consistently throw NotSupportException
  [HttpKernel] Clarify error handler restoring process again
  [HttpClient] Remove CURLOPT_CONNECTTIMEOUT_MS curl opt
  add missing conflict rule
  [Intl] fix nullable phpdocs and useless method visibility of internal class
  remove some more useless phpdocs
  Resilience against file_get_contents() race conditions.
  Turned return type annotations of private methods into php return types.

Author: nicolas-grekas

FormFieldRegistry.php

@@ -154,10 +154,8 @@ private static function create(string $base, array $values)
 
     /**
      * Transforms a PHP array in a list of fully qualified name / value.
-     *
-     * @return array The list of fields as [string] Fully qualified name => (mixed) value)
      */
-    private function walk(array $array, ?string $base = '', array &$output = [])
+    private function walk(array $array, ?string $base = '', array &$output = []): array
     {
         foreach ($array as $k => $v) {
             $path = empty($base) ? $k : sprintf('%s[%s]', $base, $k);
@@ -178,7 +176,7 @@ private function walk(array $array, ?string $base = '', array &$output = [])
      *
      * @return string[] The list of segments
      */
-    private function getSegments(string $name)
+    private function getSegments(string $name): array
     {
         if (preg_match('/^(?P<base>[^[]+)(?P<extra>(\[.*)|$)/', $name, $m)) {
             $segments = [$m['base']];