[Translator][FrameworkBundle] Added @ to the list of allowed chars in Translator
Merge branch '2.3' into 2.4

* 2.3:
  [Translator] Use quote to surround invalid locale
  Optimize assertLocale regexp
  [Validator] Backported #11410 to 2.3: Object initializers are called only once per object
  [Translator][FrameworkBundle] Added @ to the list of allowed chars in Translator
  [Process] Reduce I/O load on Windows platform
  [Form] Check if IntlDateFormatter constructor returned a valid object before using it