Use ECMGenerateExportHeader to manage deprecated API better

Allows

• projects linking to KRunner to hide deprecated API up to a given version or silence deprecation warnings after a given version, using
  • -DKRUNNER_DISABLE_DEPRECATED_BEFORE_AND_AT
  • -DKRUNNER_NO_DEPRECATED
  • -DKRUNNER_DEPRECATED_WARNINGS_SINCE
  • -DKRUNNER_NO_DEPRECATED_WARNINGS
    
    or
  • -DKF_DISABLE_DEPRECATED_BEFORE_AND_AT
  • -DKF_NO_DEPRECATED
  • -DKF_DEPRECATED_WARNINGS_SINCE
  • -DKF_NO_DEPRECATED_WARNINGS