[Windows] Fix for Argument Exception raised when the GetStringSize method of ICanvas called with default font

src/Controls/tests/TestCases.HostApp/Issues/Issue20419.cs

@@ -0,0 +1,40 @@
+namespace Controls.TestCases.HostApp.Issues;
+
+[Issue(IssueTracker.Github, 20419, "Argument Exception raised when the GetStringSize method of ICanvas called with default font", PlatformAffected.UWP)]
+public class Issue20419 : ContentPage
+{
+	public Issue20419()
+	{
+		VerticalStackLayout verticalStackLayout = new VerticalStackLayout();
+
+		GraphicsView graphicsView = new GraphicsView()
+		{
+			HeightRequest = 300,
+			WidthRequest = 300,
+		};
+		graphicsView.Drawable = new MyDrawable();
+
+		Label descriptionLabel = new Label()
+		{
+			AutomationId = "descriptionLabel",
+			Text = "The test passes if the app runs without crashing and fails if the app crashes",
+			HorizontalTextAlignment = TextAlignment.Center,
+			FontSize = 20
+		};
+
+		verticalStackLayout.Children.Add(descriptionLabel);
+		verticalStackLayout.Children.Add(graphicsView);
+
+		Content = verticalStackLayout;
+	}
+}
+
+public class MyDrawable : IDrawable
+{
+	public void Draw(ICanvas canvas, RectF dirtyRect)
+	{
+		Microsoft.Maui.Graphics.Font font = new Microsoft.Maui.Graphics.Font();
+		var stringSize = canvas.GetStringSize("MyString", font, 32);
+		canvas.DrawString($"String Width: { stringSize.Width}, String Height: {stringSize.Height}", dirtyRect.Left + dirtyRect.Width / 2, dirtyRect.Top + dirtyRect.Height / 2, HorizontalAlignment.Center);
+	}
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue20419.cs

@@ -0,0 +1,21 @@
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+
+public class Issue20419 : _IssuesUITest
+{
+	public Issue20419(TestDevice device) : base(device)
+	{
+	}
+
+	public override string Issue => "Argument Exception raised when the GetStringSize method of ICanvas called with default font";
+
+	[Test]
+	[Category(UITestCategories.GraphicsView)]
+	public void Issue20419ArgumentException()
+	{
+		App.WaitForElement("descriptionLabel");
+	}
+}

src/Graphics/src/Graphics/Platforms/Windows/FontExtensions.cs

@@ -1,5 +1,6 @@
 using Microsoft.Graphics.Canvas.Text;
 using Windows.UI.Text;
+using System;
 #if NETFX_CORE
 using Windows.UI.Xaml.Media;
 #else
@@ -28,7 +29,8 @@ public static CanvasTextFormat ToCanvasTextFormat(this IFont font, float size)
 			{
 				FontFamily = font?.Name ?? FontFamily.XamlAutoFontFamily.Source,
 				FontSize = size,
-				FontWeight = new FontWeight { Weight = (ushort)(font?.Weight ?? FontWeights.Regular) },
+				// Ensure font weight stays within the valid range (1–999) to avoid runtime errors
+				FontWeight = new FontWeight { Weight = (ushort)Math.Clamp(font?.Weight ?? FontWeights.Regular, 1, 999) },
 				FontStyle = (font?.StyleType ?? FontStyleType.Normal).ToFontStyle()
 			};
 	}

src/Graphics/src/Graphics/Platforms/Windows/PlatformStringSizeService.cs

@@ -1,6 +1,5 @@
 using Microsoft.Graphics.Canvas;
 using Microsoft.Graphics.Canvas.Text;
-using Windows.UI.Text;
 
 #if MAUI_GRAPHICS_WIN2D
 namespace Microsoft.Maui.Graphics.Win2D
@@ -24,15 +23,8 @@ public SizeF GetStringSize(string value, IFont font, float textSize)
 
 		public SizeF GetStringSize(string value, IFont font, float textSize, HorizontalAlignment horizontalAlignment, VerticalAlignment verticalAlignment)
 		{
-			var format = new CanvasTextFormat
-			{
-				FontFamily = font.Name,
-				FontSize = textSize,
-				FontWeight = new FontWeight { Weight = (ushort)font.Weight },
-				FontStyle = font.StyleType.ToFontStyle(),
-				WordWrapping = CanvasWordWrapping.NoWrap
-			};
-
+			var format = font.ToCanvasTextFormat(textSize);
+
 			var device = CanvasDevice.GetSharedDevice();
 			var textLayout = new CanvasTextLayout(device, value, format, 0.0f, 0.0f);
 			textLayout.VerticalAlignment = verticalAlignment switch