Merge branch '7.4' into 8.0

* 7.4:
  [Translation] Make the extractor alias optional
  [Cache] Fix accepting named closures as early-expiration callbacks
  [Mime] Update mime types
  [HttpKernel] Conflict with symfony/flex < 2.10
  [Yaml] Align unquoted multiline scalar parsing with spec for comments
  work around limitation in JsonResponse when the data is null
  do not use recipient phone numbers as sender e-mail addresses
  [Dotenv] DotenvDumpCommand cannot be internal

Author: nicolas-grekas