The engine does complicated logig in order to provide a pre rendered icon.
However in combination with IconItem this also resulted in bugs causing
overlay icons to effectively not work (correctly) [1, 2]. This exposes the name and pixmap
properties in the data engine as in the specification [3]. Displaying of the data
is now done at the correct layer. The statusnotifertest is additionally extended
to make testing of all combinations of icon properties easier. For now the old
combined properties are kept for backwards compatibility but can be removed in
a later commit or in Plasma 6.
[1] https://phabricator.kde.org/D28107
[2] https://phabricator.kde.org/D27617#630440
[3] https://www.freedesktop.org/wiki/Specifications/StatusNotifierItem/StatusNotifierItem/