The end goal is to make GcalEventEditorSection require inheriting AdwPreferencesGroup. Given that most widgets utilizing GcalEventEditorSection inherit another widget, we first want to change and adapt the inheritance, and then bump the requirement of the interface. These changes will be made incrementally, starting with GcalNotesSection. Part-of: <https://gitlab.gnome.org/GNOME/gnome-calendar/-/merge_requests/781>