Support rendering at non-integer display scales:

* 2x and 3x DPI artwork can be specified using
  Image2x and Image3x in chrome.yaml.
* Images are rendered using bilinear interpolation.
* For non-integer screen scales, prefer downscaling
  the next biggest resolution image over upscaling.

mods/modcontent/chrome.yaml

@@ -1,5 +1,7 @@
 ^Chrome:
 	Image: chrome.png
+	Image2x: chrome-2x.png
+	Image3x: chrome-3x.png
 
 panel-header:
 	Inherits: ^Chrome

mods/modcontent/mod.yaml

@@ -28,6 +28,8 @@ Notifications:
 
 LoadScreen: ModContentLoadScreen
 	Image: ./mods/modcontent/chrome.png
+	Image2x: ./mods/modcontent/chrome-2x.png
+	Image3x: ./mods/modcontent/chrome-3x.png
 
 ChromeMetrics:
 	common|metrics.yaml