D23815: [KConfig] port away from deprecated methods in Qt 5.14

[Volker Krause]

vkrause accepted this revision.
This revision is now accepted and ready to land.

REPOSITORY
  R237 KConfig

BRANCH
  master

REVISION DETAIL
  https://phabricator.kde.org/D23815

To: dfaure, mdawson, arichardson, vkrause
Cc: pino, arojas, mlaurent, kde-frameworks-devel, LeGast00n, GB_2, michaelh, 
ngraham, bruns