### Godot version

4.1.1

### System information

windows 11

### Issue description

When registering a type with class_name and using that class name to declare a variable in code only, autocomplete works as expected anywhere in other nodes/scenes. However, if making a custom scene node that extends a script with the class_name, if that custom scene is instantiated in a different scene, even if the type is specified, it only shows the parent node's functions and not any of the extended functionality. I have made a basic project showing the issue

### Steps to reproduce

I have made a very simple project showing the issue. https://github.com/mmmmmmmmmmmmmmmmmmmdonuts/godot_4_autocomplete_issue essentially, the extended Node scene will only show the custom function when both the type is specified as well as the type afterwards following "as" 
e.g. `@onready var my_class_4: MyClass = $MyClass4 as MyClass`

### Minimal reproduction project

https://github.com/mmmmmmmmmmmmmmmmmmmdonuts/godot_4_autocomplete_issue
counter(p_counter) {
		(*counter)++;
	}
	~RecursionCheck() {
		(*counter)--;
	}
};
static bool _guess_identifier_type(GDScriptParser::CompletionContext &p_context, const GDScriptParser::IdentifierNode *p_identifier, GDScriptCompletionIdentifier &r_type);
static bool _guess_identifier_type_from_base(GDScriptParser::CompletionContext &p_context, const GDScriptCompletionIdentifier &p_base, const StringName &p_identifier, GDScriptCompletionIdentifier &r_type);
static bool _guess_method_return_type_from_base(GDScriptParser::CompletionContext &p_context, const GDScriptCompletionIdentifier &p_base, const StringName &p_method, GDScriptCompletionIdentifier &r_type);
static bool _is_expression_named_identifier(const GDScriptParser::ExpressionNode *p_expression, const StringName &p_name) {
	if (p_expression) {
		switch (p_expression->type) {
			case GDScriptParser::Node::IDENTIFIER: {
				const GDScriptParser::IdentifierNode *id = static_cast<const GDScriptParser::IdentifierNode *>(p_expression);
				if (id->name == p_name) {
					return true;
				}
			} break;
			case GDScriptParser::Node::CAST: {
				const GDScriptParser::CastNode *cn = static_cast<const GDScriptParser::CastNode *>(p_expression);
				return _is_expression_named_identifier(cn->operand, p_name);
			} break;
			default:
				break;
		}
	}
	return false;
}
static bool _guess_expression_type(GDScriptParser::CompletionContext &p_context, const GDScriptParser::ExpressionNode *p_expression, GDScriptCompletionIdentifier &r_type) {