qml: use attached `Screen` and get rid of `screen` property in `MainCtx`
MainCtx
already provides the main window. If it is really necessary, main window's screen can be accessed through the main window.
Qt Quick already provides Screen
as an attached object, which seems to provide the required details such as desktopAvailableWidth
and devicePixelRatio
.
I have tested this with compositor_x11
, I have not observed any side effect.