ScaleFactor determination via system font size does not work with Java 9

[FStupar]

Getting the system font via Toolkit.getDefaultToolkit().getDesktopProperty("win.messagebox.font");

will return 12 no matter how scaled the display is.
I would like to either make a pull request for Java 9 using getDefaultToolkit().getScreenResolution() (which returns correct values -> 96 scaled by the percentage how much the display is enlarged) or you could implement the change (since i'm sure you know your code much better than i do :) )

EDIT: there already is the getScreenScale() method which now works on Win with Java 9