[Windows] Fix ImageHandler Vertical&Horizontal Options with AspectFit (#30936)

* Fix `ImageHandler` Vertical&Horizontal Options with AspectFit

* Add testcases screenshots

* Add comments for added GetDesiredSize override

* Refactor GetDesiredSize and MapSourceAsync for improved aspect handling

* Adjust GetDesiredSize and MapHeight for different alignment values

* Update test case snapshots for `NoScrollbars` and `ShadowsDontRespectControlShape`

Author: morning4coffe-dev

src/Controls/tests/TestCases.Android.Tests/snapshots/android/ImageRespectsVerticalAndHorizontalOptionsWithAspectFit.png

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+namespace Maui.Controls.Sample.Issues;
+
+[Issue(IssueTracker.Github, 30403, "Image under WinUI does not respect VerticalOptions and HorizontalOptions with AspectFit", PlatformAffected.UWP)]
+public class Issue30403 : TestContentPage
+{
+	protected override void Init()
+	{
+		Title = "Issue 30403";
+
+		Content = new Grid
+		{
+			BackgroundColor = Colors.LightGray,
+			Children =
+			{
+				new Image
+				{
+					AutomationId = "TestImage",
+					Source = "dotnet_bot.png",
+					Aspect = Aspect.AspectFit,
+					VerticalOptions = LayoutOptions.Center,
+					HorizontalOptions = LayoutOptions.Center,
+				}
+			}
+		};
+	}
+}

src/Controls/tests/TestCases.HostApp/Issues/Issue30403.cs

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+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+
+public class Issue30403 : _IssuesUITest
+{
+	public Issue30403(TestDevice testDevice) : base(testDevice)
+	{
+	}
+
+	public override string Issue => "Image under WinUI does not respect VerticalOptions and HorizontalOptions with AspectFit";
+
+	[Test]
+	[Category(UITestCategories.Image)]
+	public void ImageRespectsVerticalAndHorizontalOptionsWithAspectFit()
+	{
+		App.WaitForElement("TestImage");
+
+		// Verify that the image is positioned correctly according to VerticalOptions.Center and HorizontalOptions.Center
+		// with AspectFit aspect ratio. The image should appear in the center of the Grid.
+		VerifyScreenshot();
+	}
+}