### 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)


parser->push_warning(member.variable, GDScriptWarning::GET_NODE_DEFAULT_WITHOUT_ONREADY, is_using_shorthand ? "$" : "get_node()");
						}
					}
				}
#endif
			} break;
			case GDScriptParser::ClassNode::Member::CONSTANT: {
				check_class_member_name_conflict(p_class, member.constant->identifier->name, member.constant);
				member.constant->set_datatype(resolving_datatype);
				resolve_constant(member.constant, false);
				
				for (GDScriptParser::AnnotationNode *&E : member.constant->annotations) {
					resolve_annotation(E);
					E->apply(parser, member.constant);
				}
			} break;
			case GDScriptParser::ClassNode::Member::SIGNAL: {
				check_class_member_name_conflict(p_class, member.signal->identifier->name, member.signal);
				member.signal->set_datatype(resolving_datatype);
				
				
				MethodInfo mi = MethodInfo(member.signal->identifier->name);
				for (int j = 0; j < member.signal->parameters.size(); j++) {
					GDScriptParser::ParameterNode *param = member.signal->parameters[j];
					GDScriptParser::DataType param_type = type_from_metatype(resolve_datatype(param->datatype_specifier));
					param->set_datatype(param_type);
					mi.arguments.push_back(PropertyInfo(param_type.builtin_type, param->identifier->name));
					
				}
				member.signal->set_datatype(make_signal_type(mi));