Merge branch '4.4'

* 4.4:
  [Form][Validator][Intl] Fix tests
  [Messenger] return empty envelopes when RetryableException occurs
  [Intl] Excludes locale from language codes (split localized language names)
  [FrameworkBundle] WebTestCase KernelBrowser::getContainer null return type
  [Intl] Fix compile type errors
  [Validator] Accept underscores in the URL validator as the URL will resolve correctly
  [Translation] Collect original locale in case of fallback translation
  Add types to constructors and private/final/internal methods (Batch I)
  [HttpFoundation] optimize normalization of headers
  Replace REMOTE_ADDR in trusted proxies with the current REMOTE_ADDR
  [ErrorHandler] Forward \Throwable
  Fix toolbar load when GET params are present in "_wdt" route

Author: nicolas-grekas

Constraints/UrlValidator.php

@@ -25,7 +25,7 @@ class UrlValidator extends ConstraintValidator
             (%s)://                                 # protocol
             (([\.\pL\pN-]+:)?([\.\pL\pN-]+)@)?      # basic auth
             (
-                ([\pL\pN\pS\-\.])+(\.?([\pL\pN]|xn\-\-[\pL\pN-]+)+\.?) # a domain name
+                ([\pL\pN\pS\-\_\.])+(\.?([\pL\pN]|xn\-\-[\pL\pN-]+)+\.?) # a domain name
                     |                                                 # or
                 \d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}                    # an IP address
                     |                                                 # or

Tests/Constraints/LanguageValidatorTest.php

@@ -73,7 +73,6 @@ public function getValidLanguages()
     {
         return [
             ['en'],
-            ['en_US'],
             ['my'],
         ];
     }

Tests/Constraints/UrlValidatorTest.php

@@ -102,6 +102,8 @@ public function getValidUrls()
             ['http://www.example.museum'],
             ['https://example.com/'],
             ['https://example.com:80/'],
+            ['http://examp_le.com'],
+            ['http://www.sub_domain.examp_le.com'],
             ['http://www.example.coop/'],
             ['http://www.test-example.com/'],
             ['http://www.symfony.com/'],
@@ -235,7 +237,6 @@ public function getInvalidUrls()
             ['://example.com'],
             ['http ://example.com'],
             ['http:/example.com'],
-            ['http://examp_le.com'],
             ['http://example.com::aa'],
             ['http://example.com:aa'],
             ['ftp://example.fr'],