adjust screen scale for some ios devices

Runtime/Plugins/platform/ios/DeviceScreen.mm

 #import <UIKit/UIKit.h>
+#import "UIWidgetsDevice.h"
-    int IOSDeviceScaleFactor()
+    float IOSDeviceScaleFactor()
-        return [[UIScreen mainScreen] scale];
+        float scale = [[UIScreen mainScreen] scale] * 1.0;
+        if ([UIWidgetsDevice NeedScreenDownSample]) {
+            scale *= 0.8696;
+        }
+        return scale;
     }
 }

Runtime/engine/DisplayMetrics.cs

 
 #if UNITY_IOS
         [DllImport("__Internal")]
-        static extern int IOSDeviceScaleFactor();
+        static extern float IOSDeviceScaleFactor();
 
 		[DllImport("__Internal")]
 		static extern viewMetrics IOSGetViewportPadding();