Compiler permits subclasses to hide inherited built-in properties

Declaring a property in a subclass with the same name as an inherited built-in property is incorrectly accepted. The subclass property captures reads and writes without updating the built-in state, so code can appear to work while the underlying control behaves incorrectly. For example, a custom ListBox.ColumnCount setter runs, but the native ListBox columns are never created. The compiler should reject inherited built-in property hiding just as it already rejects hiding properties declared by user classes.