shell: Port DesktopView to layer-shell
This ports the DesktopView from the plasma-shell protocol to the layer-shell protocol.
There's one small caveat about the layer-shell protocol: the layer surface is bound to the output, in order to move a DesktopView between outputs, the DesktopView's visibility must be toggled to re-create the layer surface with the new output.
depends on !2790 (merged)
Edited by Vlad Zahorodnii