ContainmentConfigView has a special code path for wallpaper configs
where, if you change wallpaper type, it will create a temporary config
ConfigPropertyMap, then copy it over to the real config when the
containment actually changes.
ConfigPropertyMap does not call valueChanged() on insertion (See
QQmlPropertyMap), and we only write the value into the actual
KConfigSkeleton on valueChange.
BUG: 375532