[linux][windows] The pixel ratio is hardcoded to 1 which causes ugly rendering on high DPI displays.

[This value](https://github.com/google/flutter-desktop-embedding/blob/88f1385481f0cd1ba8ce91bfd30bc5486248f2ca/macos/library/FLEViewController.m#L317) must be determined based on the pixel ratio of the display.