fix: Disable assembly loading feature in XamlSchemaContext

Author: jeromelaban

src/SourceGenerators/System.Xaml/System.Xaml/XamlSchemaContext.cs

@@ -22,6 +22,9 @@
 //
 // History:
 // - 2021/02/21 ([email protected]): Adjust for hard link to AppDomain.AssemblyLoad
+// - 2021/11/28 ([email protected]): Disable assembly loading for Uno's as loaded types are never used.
+
+// #define SUPPORTS_LOAD_ASSEMBLIES
 
 using System;
 using System.Collections.Generic;
@@ -74,6 +77,7 @@ public XamlSchemaContext (IEnumerable<Assembly> referenceAssemblies, XamlSchemaC
 
 		private void RegisterAssemblyLoaded()
 		{
+#if SUPPORTS_LOAD_ASSEMBLIES
 			var that = new WeakReference<XamlSchemaContext>(this);
 
 			void Hook(object o, AssemblyLoadEventArgs e)
@@ -95,12 +99,15 @@ void Hook(object o, AssemblyLoadEventArgs e)
 			// Register the Hook method to the AssemblyLoad event, so there's no
 			// hard link between "this" and the AssemblyLoad event delegate.
 			AppDomain.CurrentDomain.AssemblyLoad += Hook;
+#endif
 		}
 
 		~XamlSchemaContext ()
 		{
+#if SUPPORTS_LOAD_ASSEMBLIES
 			if (reference_assemblies == null)
 				unhookAssemblyLoad?.Invoke();
+#endif
 		}
 
 		IList<Assembly> reference_assemblies;
@@ -321,6 +328,7 @@ public virtual bool TryGetCompatibleXamlNamespace (string xamlNamespace, out str
 			}
 		}
 
+#if SUPPORTS_LOAD_ASSEMBLIES
 		void OnAssemblyLoaded (object o, AssemblyLoadEventArgs e)
 		{
 			if (reference_assemblies != null)
@@ -335,6 +343,7 @@ void OnAssemblyLoaded (object o, AssemblyLoadEventArgs e)
 			if (all_xaml_types != null)
 				FillAllXamlTypes (e.LoadedAssembly);
 		}
+#endif
 
 		// cache updater methods
 		void FillXamlNamespaces (Assembly ass)