Fix for AccessText underlines being very blurry since they didn't align to pixels.

src/Avalonia.Controls/Primitives/AccessText.cs

@@ -3,6 +3,7 @@ using Avalonia.Input;
 using Avalonia.Reactive;
 using Avalonia.Media;
 using Avalonia.Media.TextFormatting;
+using System;
 
 namespace Avalonia.Controls.Primitives
 {
@@ -68,11 +69,15 @@ namespace Avalonia.Controls.Primitives
             if (underscore != -1 && ShowAccessKey)
             {
                 var rect = TextLayout!.HitTestTextPosition(underscore);
-                var offset = new Vector(0, -1.5);
+
+                var x1 = Math.Round(rect.Left, MidpointRounding.AwayFromZero);
+                var x2 = Math.Round(rect.Right, MidpointRounding.AwayFromZero);
+                var y = Math.Round(rect.Bottom, MidpointRounding.AwayFromZero) - 1.5;
+
                 context.DrawLine(
                     new Pen(Foreground, 1),
-                    rect.BottomLeft + offset,
-                    rect.BottomRight + offset);
+                    new Point(x1, y),
+                    new Point(x2, y));
             }
         }