Use Symfony Request for language module

Part of #1998638: [Meta] Refactor raw PHP variables (e.g $_SERVER, $_REQUEST, $_GET, $_POST) with Symfony Request object

Files that need converting are:

• core/modules/language/language.negotiation.inc
• core/modules/language/lib/Drupal/language/Tests/LanguageBrowserDetectionUnitTest.php
• core/modules/language/lib/Drupal/language/Tests/LanguageUILanguageNegotiationTest.php
• core/modules/language/lib/Drupal/language/Tests/LanguageUrlRewritingTest.php
• core/modules/language/tests/language_test/lib/Drupal/language_test/LanguageTestManager.php