### Godot version

4.1.beta3

### System information

Fedora Workstation 38 - Godot 4.1.beta3 - Vulkan (Forward+)

### Issue description

**This is an issue created by the production team, we're working on it**

Currently, it's impossible to call virtual functions within GDScript.

This currently returns an error:
```gdscript
# a.gd
extends Node

func _process(delta: float) -> void:
	pass
```

```gdscript
# main.gd
extends Node

var my_node: Node = preload("res://a.gd").new()

func _process(delta: float) -> void:
	my_node._process(delta)  # Cannot call virtual function "_process()" because it hasn't been defined.
```

### Steps to reproduce

1. Create a script (`a.gd`) based on `Node` that declares `_process()`;
2. Create a main node;
3. Attach a script to the main node;
4. Initialize a variable with a new `a.gd` instance;
5. Try to run `_process()` on that node;
6. Find out that it returns an error.

### Minimal reproduction project

[virtual_functions.zip (updated)](https://github.com/godotengine/godot/files/11823992/virtual_functions.zip)


case Variant::ARRAY:
							case Variant::STRING:
								error = index_type.builtin_type != Variant::INT && index_type.builtin_type != Variant::FLOAT;
								break;
							
							case Variant::RECT2:
							case Variant::RECT2I:
							case Variant::PLANE:
							case Variant::QUATERNION:
							case Variant::AABB:
							case Variant::OBJECT:
								error = index_type.builtin_type != Variant::STRING && index_type.builtin_type != Variant::STRING_NAME;
								break;
							
							case Variant::BASIS:
							case Variant::VECTOR2:
							case Variant::VECTOR2I:
							case Variant::VECTOR3:
							case Variant::VECTOR3I:
							case Variant::VECTOR4:
							case Variant::VECTOR4I:
							case Variant::TRANSFORM2D:
							case Variant::TRANSFORM3D:
							case Variant::PROJECTION:
								error = index_type.builtin_type != Variant::INT && index_type.builtin_type != Variant::FLOAT &&
										index_type.builtin_type != Variant::STRING && index_type.builtin_type != Variant::STRING_NAME;
								break;
							
							case Variant::COLOR:
								error = index_type.builtin_type != Variant::INT && index_type.builtin_type != Variant::STRING && index_type.builtin_type != Variant::STRING_NAME;