### 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_subscript->reduced_value = p_subscript->attribute->reduced_value;
			} else if (!base_type.is_meta_type || !base_type.is_constant) {
				valid = base_type.kind != GDScriptParser::DataType::BUILTIN;
#ifdef DEBUG_ENABLED
				if (valid) {
					parser->push_warning(p_subscript, GDScriptWarning::UNSAFE_PROPERTY_ACCESS, p_subscript->attribute->name, base_type.to_string());
				}
#endif
				result_type.kind = GDScriptParser::DataType::VARIANT;
				mark_node_unsafe(p_subscript);
			}
		}
		if (!valid) {
			GDScriptParser::DataType attr_type = p_subscript->attribute->get_datatype();
			if (!p_can_be_pseudo_type && (attr_type.is_pseudo_type || result_type.is_pseudo_type)) {
				push_error(vformat(R"(Type "%s" in base "%s" cannot be used on its own.)", p_subscript->attribute->name, type_from_metatype(base_type).to_string()), p_subscript->attribute);
			} else {
				push_error(vformat(R"(Cannot find member "%s" in base "%s".)", p_subscript->attribute->name, type_from_metatype(base_type).to_string()), p_subscript->attribute);
			}
			result_type.kind = GDScriptParser::DataType::VARIANT;
		}
	} else {
		if (p_subscript->index == nullptr) {
			return;
		}
		reduce_expression(p_subscript->index);
		if (p_subscript->base->is_constant && p_subscript->index->is_constant) {
			
			bool valid = false;
			Variant value = p_subscript->base->reduced_value.get(p_subscript->index->reduced_value, &valid);