### 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)


if (base_type.kind != GDScriptParser::DataType::BUILTIN) {
					base_type.builtin_type = Variant::OBJECT;
				}
				switch (base_type.builtin_type) {
					
					case Variant::RID:
					case Variant::BOOL:
					case Variant::CALLABLE:
					case Variant::FLOAT:
					case Variant::INT:
					case Variant::NIL:
					case Variant::NODE_PATH:
					case Variant::SIGNAL:
					case Variant::STRING_NAME:
						result_type.kind = GDScriptParser::DataType::VARIANT;
						push_error(vformat(R"(Cannot use subscript operator on a base of type "%s".)", base_type.to_string()), p_subscript->base);
						break;
					
					case Variant::PACKED_BYTE_ARRAY:
					case Variant::PACKED_INT32_ARRAY:
					case Variant::PACKED_INT64_ARRAY:
					case Variant::VECTOR2I:
					case Variant::VECTOR3I:
					case Variant::VECTOR4I:
						result_type.builtin_type = Variant::INT;
						break;
					
					case Variant::PACKED_FLOAT32_ARRAY:
					case Variant::PACKED_FLOAT64_ARRAY:
					case Variant::VECTOR2: