[XSG] enable diagnostis by default on Debug (#32052)

if EnableDiagnostics isn't set, defaut to true on Debug builds

- fixes #32047

Author: StephaneDelcroix

src/Controls/src/Build.Tasks/nuget/buildTransitive/netstandard2.0/Microsoft.Maui.Controls.Common.targets

@@ -29,5 +29,6 @@
 		<CompilerVisibleItemMetadata Include="AdditionalFiles" MetadataName="EnableDiagnostics" />
     <CompilerVisibleProperty Include="MauiXamlLineInfo" />
 		<CompilerVisibleItemMetadata Include="AdditionalFiles" MetadataName="LineInfo" />
+    <CompilerVisibleProperty Include="Configuration" />
 	</ItemGroup>
 </Project>

src/Controls/src/SourceGen/ProjectItem.cs

@@ -32,7 +32,11 @@ public bool EnableDiagnostics
 				return true;
 			if (Options.IsFalse("build_metadata.additionalfiles.EnableDiagnostics"))
 				return false;
-			return Options.IsTrue("build_property.EnableMauiXamlDiagnostics");
+			if (Options.IsTrue("build_property.EnableMauiXamlDiagnostics"))
+				return true;
+			if (Options.IsFalse("build_property.EnableMauiXamlDiagnostics"))
+				return false;
+			return !Configuration.Equals("Release", StringComparison.OrdinalIgnoreCase);
 		}
 	}