### 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_binary_op->variant_op == Variant::OP_DIVIDE && left_type.builtin_type == Variant::INT && right_type.builtin_type == Variant::INT) {
		parser->push_warning(p_binary_op, GDScriptWarning::INTEGER_DIVISION);
	}
#endif
	if (p_binary_op->left_operand->is_constant && p_binary_op->right_operand->is_constant) {
		p_binary_op->is_constant = true;
		if (p_binary_op->variant_op < Variant::OP_MAX) {
			bool valid = false;
			Variant::evaluate(p_binary_op->variant_op, p_binary_op->left_operand->reduced_value, p_binary_op->right_operand->reduced_value, p_binary_op->reduced_value, valid);
			if (!valid) {
				if (p_binary_op->reduced_value.get_type() == Variant::STRING) {
					push_error(vformat(R"(%s in operator %s.)", p_binary_op->reduced_value, Variant::get_operator_name(p_binary_op->variant_op)), p_binary_op);
				} else {
					push_error(vformat(R"(Invalid operands to operator %s, %s and %s.)",
									   Variant::get_operator_name(p_binary_op->variant_op),
									   Variant::get_type_name(p_binary_op->left_operand->reduced_value.get_type()),
									   Variant::get_type_name(p_binary_op->right_operand->reduced_value.get_type())),
							p_binary_op);
				}
			}
		} else {
			ERR_PRINT("Parser bug: unknown binary operation.");
		}
		p_binary_op->set_datatype(type_from_variant(p_binary_op->reduced_value, p_binary_op));
		return;
	}
	GDScriptParser::DataType result;
	if ((p_binary_op->variant_op == Variant::OP_EQUAL || p_binary_op->variant_op == Variant::OP_NOT_EQUAL) &&
			((left_type.kind == GDScriptParser::DataType::BUILTIN && left_type.builtin_type == Variant::NIL) || (right_type.kind == GDScriptParser::DataType::BUILTIN && right_type.builtin_type == Variant::NIL))) {