Update to use CustomMarshaller entry point type (dotnet/runtime#71398)

Commit migrated from dotnet/runtime@6c10d0e

src/System.Drawing.Common/src/Interop/Windows/Interop.Gdi32.cs

@@ -188,7 +188,7 @@ internal sealed class DOCINFO
             internal int fwType;
 
 #if NET7_0_OR_GREATER
-            [ManagedToUnmanagedMarshallers(typeof(DOCINFO), InMarshaller = typeof(Marshaller))]
+            [CustomMarshaller(typeof(DOCINFO), Scenario.ManagedToUnmanagedIn, typeof(Marshaller))]
             public static class Marshaller
             {
                 public static Native ConvertToUnmanaged(DOCINFO managed) => new(managed);