Currently, if an X11 or Wayland window is damaged, we will schedule a
repaint. This results in some code duplication that this change intends
to get rid of.
The layer-shell protocol allows wayland clients to create surfaces that
can be used for building desktop environment components such as panels,
notifications, etc.
The support for the plasma-shell protocol will be dropped once plasma in
all its entirety is ported to the layer-shell protocol.