A factory is supposed to emit this signal whenever the decorations
need to be recrated. The DecorationPlugins inside KWin Core connect
to the signal and recreate the decorations.
This signal is supposed to replace the reset method which encoded
this information in the return value and which is already ignored.
Unfortunately only information available through the factory can be read.
As Factory is not a QObject we cannot use the Q_SLOT trick to get further
information dynamically from the loaded decoration plugin.
REVIEW: 110665
This allows to move the slot to reset the decoration when compositing
got toggled from Workspace to DecorationPlugin and the custom cleanup
is no longer needed.
REVIEW: 109909
