### 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)


p_type->set_datatype(result);
		return result;
	}
	StringName first = p_type->type_chain[0]->name;
	if (first == SNAME("Variant")) {
		if (p_type->type_chain.size() == 2) {
			
			StringName enum_name = p_type->type_chain[1]->name;
			StringName qualified_name = String(first) + ENUM_SEPARATOR + String(p_type->type_chain[1]->name);
			if (CoreConstants::is_global_enum(qualified_name)) {
				result = make_global_enum_type(enum_name, first, true);
				return result;
			} else {
				push_error(vformat(R"(Name "%s" is not a nested type of "Variant".)", enum_name), p_type->type_chain[1]);
				return bad_type;
			}
		} else if (p_type->type_chain.size() > 2) {
			push_error(R"(Variant only contains enum types, which do not have nested types.)", p_type->type_chain[2]);
			return bad_type;
		}
		result.kind = GDScriptParser::DataType::VARIANT;
	} else if (first == SNAME("Object")) {
		
		result.kind = GDScriptParser::DataType::NATIVE;
		result.builtin_type = Variant::OBJECT;
		result.native_type = SNAME("Object");
	} else if (GDScriptParser::get_builtin_type(first) < Variant::VARIANT_MAX) {
		
		if (p_type->type_chain.size() > 1) {
			push_error(R"(Built-in types don't contain nested types.)", p_type->type_chain[1]);