Merge branch '5.3' into 5.4

* 5.3:
  [Tests] Remove some unused fixtures
  added missing translations for portuguese [#43726]
  [HttpClient][Mime] Add correct IDN flags for IDNA2008 compliance
  properly parse quoted strings tagged with !!str
  do not merge label classes into expanded choice labels
  [Serializer] PropertyNormalizer - return unique (i.e. filter duplicate ) attributes in extractAttributes function

Author: derrabus