### Godot version

v4.2.rc.mono.custom_build [ad72de508]

### System information

Windows 10

### Issue description

As I pointed out several times earlier in [#80284](https://github.com/godotengine/godot/pull/80284#issuecomment-1722120503), the references to singletons in `GDScript` are still not updated after the `GDExtension` reload.

https://github.com/godotengine/godot/assets/7782218/f90052a5-0de2-4310-8235-f0b9e2f74b3a

Singletons themselves are updated and work correctly, but references to these singletons are not updated in `@tool` scripts. That is, `Engine.get_singleton` returns the actual working reference, but using the singleton directly through its name causes errors.

### Steps to reproduce

* Clone `4.2.reload_singleton` branch from the MRP repository https://github.com/DmitriySalnikov/gde_test_cases/tree/4.2.reload_singleton
* Build as usual
* Open the project from the `project/` folder
* Add one character to the source code and rebuild
* Focus on the editor to reload extension
* Watch for error spam when calling by singleton name

### Minimal reproduction project

https://github.com/DmitriySalnikov/gde_test_cases/tree/4.2.reload_singleton
"assert",
		"preload",
		
		"void",
		nullptr,
	};
	const char **w = _reserved_words;
	while (*w) {
		p_words->push_back(*w);
		w++;
	}
}
bool GDScriptLanguage::is_control_flow_keyword(String p_keyword) const {
	
	return p_keyword == "break" ||
			p_keyword == "continue" ||
			p_keyword == "elif" ||
			p_keyword == "else" ||
			p_keyword == "for" ||
			p_keyword == "if" ||
			p_keyword == "match" ||
			p_keyword == "pass" ||
			p_keyword == "return" ||
			p_keyword == "when" ||
			p_keyword == "while";
}
bool GDScriptLanguage::handles_global_class_type(const String &p_type) const {
	return p_type == "GDScript";
}
String GDScriptLanguage::get_global_class_name(const String &p_path, String *r_base_type, String *r_icon_path) const {