Detect method BuildAvaloniaApp in base class.

src/Avalonia.DesignerSupport/Remote/RemoteDesignerEntryPoint.cs

@@ -168,8 +168,12 @@ namespace Avalonia.DesignerSupport.Remote
             var entryPoint = asm.EntryPoint;
             if (entryPoint == null)
                 throw Die($"Assembly {args.AppPath} doesn't have an entry point");
-            var builderMethod = entryPoint.DeclaringType.GetMethod(BuilderMethodName,
-                BindingFlags.Static | BindingFlags.Public | BindingFlags.NonPublic, null, Array.Empty<Type>(), null);
+            var builderMethod = entryPoint.DeclaringType.GetMethod(
+                BuilderMethodName,
+                BindingFlags.Static | BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.FlattenHierarchy,
+                null,
+                Array.Empty<Type>(),
+                null);
             if (builderMethod == null)
                 throw Die($"{entryPoint.DeclaringType.FullName} doesn't have a method named {BuilderMethodName}");
             Design.IsDesignMode = true;