Code review comment for lp://staging/~nick-dedekind/qtmir/multiwindow.screenwindow

/me not sure why PlatformScreen better name than just Screen.

This also allows multiple windows to be associated with each screen, where before a single window (i.e. compositor) had a single screen. What does this mean now? If a screen has 2 windows, what one is rendered?

Or is it just an intermediary state while Qt is adjusting to a screen being removed?