Tested versions

Bugged in 4.0 - 4.5 beta1
Works correctly in 3.6

System information

W10

Issue description

I randomly noticed that you can use class_name in a built-in script. I recall it used to be an error, but now seems allowed and, as expected, it's not very functional (you can get a global name from the script, but that probably it).

The error in question:

I'm actually surprised this regression is so old D:

Steps to reproduce

1. Add a Node
2. Attach a built-in script
3. Add class_name

Minimal reproduction project (MRP)

N/A