### 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)


reduce_dictionary(static_cast<GDScriptParser::DictionaryNode *>(p_expression));
			break;
		case GDScriptParser::Node::GET_NODE:
			reduce_get_node(static_cast<GDScriptParser::GetNodeNode *>(p_expression));
			break;
		case GDScriptParser::Node::IDENTIFIER:
			reduce_identifier(static_cast<GDScriptParser::IdentifierNode *>(p_expression));
			break;
		case GDScriptParser::Node::LAMBDA:
			reduce_lambda(static_cast<GDScriptParser::LambdaNode *>(p_expression));
			break;
		case GDScriptParser::Node::LITERAL:
			reduce_literal(static_cast<GDScriptParser::LiteralNode *>(p_expression));
			break;
		case GDScriptParser::Node::PRELOAD:
			reduce_preload(static_cast<GDScriptParser::PreloadNode *>(p_expression));
			break;
		case GDScriptParser::Node::SELF:
			reduce_self(static_cast<GDScriptParser::SelfNode *>(p_expression));
			break;
		case GDScriptParser::Node::SUBSCRIPT:
			reduce_subscript(static_cast<GDScriptParser::SubscriptNode *>(p_expression));
			break;
		case GDScriptParser::Node::TERNARY_OPERATOR:
			reduce_ternary_op(static_cast<GDScriptParser::TernaryOpNode *>(p_expression), p_is_root);
			break;
		case GDScriptParser::Node::TYPE_TEST:
			reduce_type_test(static_cast<GDScriptParser::TypeTestNode *>(p_expression));
			break;
		case GDScriptParser::Node::UNARY_OPERATOR: