Merge branch '3.4' into 4.0

* 3.4:
  Remove symfony/polyfill-ctype where not needed
  Use symfony/polyfill-ctype
  [Form] fixes instance variable phpdoc in FormRegistry class
  bumped Symfony version to 3.4.10
  updated VERSION for 3.4.9
  updated CHANGELOG for 3.4.9
  Add CODE_OF_CONDUCT.md
  Added .github/CODEOWNERS
  bumped Symfony version to 2.8.40
  updated VERSION for 2.8.39
  updated CHANGELOG for 2.8.39

Author: nicolas-grekas

composer.json

@@ -16,7 +16,8 @@
         }
     ],
     "require": {
-        "php": "^7.1.3"
+        "php": "^7.1.3",
+        "symfony/polyfill-ctype": "~1.8"
     },
     "autoload": {
         "psr-4": { "Symfony\\Component\\Filesystem\\": "" },