Deprecate KNotification constructor taking widget parameter
While there is a plan for Knotifications V2 which would deprecate the whole current API possibly (https://phabricator.kde.org/T11875) for the case that the plan does not work out, let's maintain the current API to be prepared for living on as fallback, and handle the present KDE5 TODO note.
Plan to deprecate the other constructor was noted in 2009 after some API rework, comment added by https://commits.kde.org/kdelibs/a8f5ad0185fb259286fb113c7afffaa3f60d3e2f IMHO it makes some sense to ask for an explicit setting of the widget like already done for all the other properties. https://lxr.kde.org/search?_filestring=&_string=KNotification%5C%28&_casesensitive=1 hints there are also not many users of that constructor, so this would not go too much against people's coding.