[XSG] double cast on Add (#31367)

fixes 3 failing tests related to OnPlatform

Author: StephaneDelcroix

src/Controls/src/SourceGen/Visitors/SetPropertiesVisitor.cs

@@ -618,8 +618,13 @@ static void Add(IndentedTextWriter writer, LocalVariable parentVar, XmlName prop
 		if (receiverType is not null && !propertyType!.Equals(receiverType, SymbolEqualityComparer.Default))
 			parentObj = $"(({receiverType.ToFQDisplayString()}){parentObj})";
 
+		//look for intermediate implicit casts
+		string cast = string.Empty;
+		if (HasDoubleImplicitConversion(context.Variables[valueNode].Type, itemType, context, out var conv))
+			cast = "(" + conv!.ReturnType.ToFQDisplayString() + ")";
+
 		using (PrePost.NewLineInfo(writer, (IXmlLineInfo)valueNode, context.FilePath))
-			writer.WriteLine($"{parentObj}.Add(({itemType.ToFQDisplayString()}){context.Variables[valueNode].Name});");
+			writer.WriteLine($"{parentObj}.Add(({itemType.ToFQDisplayString()}){cast}{context.Variables[valueNode].Name});");
 	}
 
 	static void AddToResourceDictionary(IndentedTextWriter writer, LocalVariable parentVar, IElementNode node, SourceGenContext context)

src/Controls/tests/Xaml.UnitTests/Issues/Maui24900.xaml.cs

@@ -37,11 +37,7 @@ public void TearDown()
 		}
 
 		[Test]
-#if FIXME_BEFORE_PUBLIC_RELEASE
-		public void OnPlatformDoesNotThrow([Values(XamlInflator.XamlC, XamlInflator.Runtime)] XamlInflator inflator)
-#else
 		public void OnPlatformDoesNotThrow([Values] XamlInflator inflator)
-#endif
 		{
 			mockDeviceInfo.Platform = DevicePlatform.WinUI;
 			Assert.DoesNotThrow(() => new Maui24900(inflator));

src/Controls/tests/Xaml.UnitTests/Issues/Maui4509.xaml.cs

@@ -21,23 +21,15 @@ public void TearDown()
 		}
 
 		[Test]
-#if FIXME_BEFORE_PUBLIC_RELEASE
-		public void OnPlatformAsCollectionElementiOS([Values(XamlInflator.XamlC, XamlInflator.Runtime)] XamlInflator inflator)
-#else
 		public void OnPlatformAsCollectionElementiOS([Values] XamlInflator inflator)
-#endif
 		{
 			DeviceInfo.SetCurrent(new MockDeviceInfo(platform: DevicePlatform.iOS));
 			var page = new Maui4509(inflator);
 			Assert.That(page.layout.Children.Count, Is.EqualTo(2));
 		}
 
 		[Test]
-#if FIXME_BEFORE_PUBLIC_RELEASE
-		public void OnPlatformAsCollectionElementAndroid([Values(XamlInflator.XamlC, XamlInflator.Runtime)] XamlInflator inflator)
-#else
 		public void OnPlatformAsCollectionElementAndroid([Values] XamlInflator inflator)
-#endif
 		{
 			DeviceInfo.SetCurrent(new MockDeviceInfo(platform: DevicePlatform.Android));
 			var page = new Maui4509(inflator);