Update src/Symfony/Component/HttpFoundation/Request.php

This makes `getContentType()` work when a regular form is submitted.
[Form] Choice children can be template customized like collection
[Serializer] Added PropertyNormalizer, a new normalizer that maps an object's properties to an array
Call AuthenticationManager in AnonymousAuthenticationListener
[HttpKernel] Extract method to make callable controller in ControllerResolver

correct naming
SSI support
Disallow abstract definitions from doctrine event listener registration
[HttpFoundation] ResponseHeaderBag::clearCookie now accepts secure/httpOnly
Add missing dot at the end of an exception message
Added line feed to container alias description (text descriptor)
New service to simplify password encoding
[Form] Check if IntlDateFormatter constructor returned a valid object before using it
ISSUE #11300: Improve Routing Syntax Import Error

modified FileLoaderLoadException message to present the previous (Parse)Exception first
Add test and small code fix
Added support for encoding and decoding namespaced xml (xmlns)
server:run command: provide more error information

The server:run command didn't provide many information when the executed
command exited unexpectedly. Now, the process' exit code is passed through
and an error message is displayed.
[Process] Reduce I/O load on Windows platform
[Translator][FrameworkBundle] Added @ to the list of allowed chars in Translator
bug #11403 [Translator][FrameworkBundle] Added @ to the list of allowed chars in Translator (takeit)

This PR was squashed before being merged into the 2.3 branch (closes #11403).

Discussion
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[Translator][FrameworkBundle] Added @ to the list of allowed chars in Translator

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #11396
| License       | MIT

Commits
-------

3176f8b [Translator][FrameworkBundle] Added @ to the list of allowed chars in Translator
[Validator] Backported #11410 to 2.3: Object initializers are called only once per object