Merge branch '6.3' into 6.4

* 6.3:
  [AssetMapper] Fixing import parsing from jsdelivr
  Fix htaccess sample to use index.php instead of app.php
  [SecurityBundle] Add `firewalls.logout.csrf_token_manager` to XSD
  [Form] Fix form events phpdocs
  fix(mailgun-smtp): disable tls for mailgun as it should use starttls instead

Author: derrabus

ServerBag.php

@@ -49,7 +49,7 @@ public function getHeaders(): array
              * RewriteCond %{HTTP:Authorization} .+
              * RewriteRule ^ - [E=HTTP_AUTHORIZATION:%0]
              * RewriteCond %{REQUEST_FILENAME} !-f
-             * RewriteRule ^(.*)$ app.php [QSA,L]
+             * RewriteRule ^(.*)$ index.php [QSA,L]
              */
 
             $authorizationHeader = null;