Port tooltips to KToolTipWidget
Summary:
KToolTipWidget (introduced by kwidgetsaddons 5.30) supersedes the
tooltip code (originally forked from Dolphin) in kinfocenter.
Test Plan: Tooltips still work, both in X11 and Wayland.
Reviewers: Plasma
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D4566