because Q_DECLARE_PUBLIC() declares class clangs emmits warning that the
classes were previously declared as structs, this change is kinda of revert
of previous series of struct <-> class warnings fixes and may need changes
in other places (such as konsole from kde-baseapps) to fix the same issues
given that now the forementioned classes declaration has changed
Signed-off-by: Ivailo Monev <xakepa10@gmail.com>