### 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)


bool is_valid = false;
		Variant value = base_value.get(index_value, &is_valid);
		if (is_valid) {
			is_reduced = true;
			return value;
		} else {
			return Variant();
		}
	}
}
Array GDScriptAnalyzer::make_array_from_element_datatype(const GDScriptParser::DataType &p_element_datatype, const GDScriptParser::Node *p_source_node) {
	Array array;
	if (p_element_datatype.builtin_type == Variant::OBJECT) {
		Ref<Script> script_type = p_element_datatype.script_type;
		if (p_element_datatype.kind == GDScriptParser::DataType::CLASS && script_type.is_null()) {
			Error err = OK;
			Ref<GDScript> scr = GDScriptCache::get_shallow_script(p_element_datatype.script_path, err);
			if (err) {
				push_error(vformat(R"(Error while getting cache for script "%s".)", p_element_datatype.script_path), p_source_node);
				return array;
			}
			script_type.reference_ptr(scr->find_class(p_element_datatype.class_type->fqcn));
		}
		array.set_typed(p_element_datatype.builtin_type, p_element_datatype.native_type, script_type);
	} else {
		array.set_typed(p_element_datatype.builtin_type, StringName(), Variant());
	}
	return array;
}
Variant GDScriptAnalyzer::make_variable_default_value(GDScriptParser::VariableNode *p_variable) {