### 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 (p_subscript->base == nullptr || p_subscript->index == nullptr) {
		return Variant();
	}
	bool is_base_value_reduced = false;
	Variant base_value = make_expression_reduced_value(p_subscript->base, is_base_value_reduced);
	if (!is_base_value_reduced) {
		return Variant();
	}
	if (p_subscript->is_attribute) {
		bool is_valid = false;
		Variant value = base_value.get_named(p_subscript->attribute->name, is_valid);
		if (is_valid) {
			is_reduced = true;
			return value;
		} else {
			return Variant();
		}
	} else {
		bool is_index_value_reduced = false;
		Variant index_value = make_expression_reduced_value(p_subscript->index, is_index_value_reduced);
		if (!is_index_value_reduced) {
			return Variant();
		}