Suppress Obsolete warnings in the ComInterfaceGenerator (#88859)

Author: jkoritzinsky

src/libraries/System.Runtime.InteropServices/gen/ComInterfaceGenerator/ComInterfaceGenerator.cs

@@ -169,6 +169,7 @@ public void Initialize(IncrementalGeneratorInitializationContext context)
 
                     using StringWriter source = new();
                     source.WriteLine("// <auto-generated />");
+                    source.WriteLine("#pragma warning disable CS0612, CS0618"); // Suppress warnings about [Obsolete] member usage in generated code.
                     interfaceInfo.WriteTo(source);
                     // Two newlines looks cleaner than one
                     source.WriteLine();