### 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 (!list_type.is_hard_type()) {
			mark_node_unsafe(p_for->list);
		}
		if (list_type.is_variant()) {
			variable_type.kind = GDScriptParser::DataType::VARIANT;
			mark_node_unsafe(p_for->list);
		} else if (list_type.has_container_element_type()) {
			variable_type = list_type.get_container_element_type();
			variable_type.type_source = list_type.type_source;
		} else if (list_type.is_typed_container_type()) {
			variable_type = list_type.get_typed_container_type();
			variable_type.type_source = list_type.type_source;
		} else if (list_type.builtin_type == Variant::INT || list_type.builtin_type == Variant::FLOAT || list_type.builtin_type == Variant::STRING) {
			variable_type.type_source = list_type.type_source;
			variable_type.kind = GDScriptParser::DataType::BUILTIN;
			variable_type.builtin_type = list_type.builtin_type;
		} else if (list_type.builtin_type == Variant::VECTOR2I || list_type.builtin_type == Variant::VECTOR3I) {
			variable_type.type_source = list_type.type_source;
			variable_type.kind = GDScriptParser::DataType::BUILTIN;
			variable_type.builtin_type = Variant::INT;
		} else if (list_type.builtin_type == Variant::VECTOR2 || list_type.builtin_type == Variant::VECTOR3) {
			variable_type.type_source = list_type.type_source;
			variable_type.kind = GDScriptParser::DataType::BUILTIN;
			variable_type.builtin_type = Variant::FLOAT;
		} else if (list_type.builtin_type == Variant::OBJECT) {
			GDScriptParser::DataType return_type;
			List<GDScriptParser::DataType> par_types;
			int default_arg_count = 0;
			BitField<MethodFlags> method_flags;
			if (get_function_signature(p_for->list, false, list_type, CoreStringNames::get_singleton()->_iter_get, return_type, par_types, default_arg_count, method_flags)) {