UI confused when window moved between screens that have different pixel density
When there are multiple screens available, it is possible that the Doomsday window is moved between screens whose pixel density is different. In this case, the change in pixel ratio must be detected and the UI must be updated accordingly.
This requires making the pixel ratio part of UI layout length rules so that its value can change dynamically. Also, the UI style package must be reloadable so that fonts can be reconfigured with the appropriate new sizes.
As a side effect, supporting dynamic pixel ratio changes will also make it possible to apply the user's custom UI scale factor on the fly without requiring a restart.