D27459: Port QLinkedList which is deprecated in qt5.15

[Laurent Montel]

mlaurent added a reviewer: dfaure.

REPOSITORY
  R263 KXmlGui

REVISION DETAIL
  https://phabricator.kde.org/D27459

To: mlaurent, dfaure
Cc: kde-frameworks-devel, LeGast00n, cblack, GB_2, michaelh, ngraham, bruns