Fix GDScript error when using an inherited const as annotation

[trollodel]

Fix a GDScript analyzer error when using as an annotation a class declared as const which is declared in the parent script (or in a relative one). Regardless the fact is not ideal, declaring again the const class in the child script raises an error because the const is already declared, preventing to workaround the issue.

Example:

# base_class.gd
const external_script = preload("external_script.gd")

func virtual_method(_ext: external_script) -> String:
	return "Base"

extends "base_class.gd"

# Error: "external_script" was not found in the current scope
func virtual_method(_ext: external_script) -> String:
	return "Subclass"

This PR includes an integration test for this issue.

[vnen]

I believe this doesn't cover enough cases, as it's not checking the inheritance tree of the inner class itself (only for the outermost class). So the proper way would be to check the inherited constants of the current class, then go the outer one and do the same, then the outer one from that and so on. It's complicated but it should solve all cases.

If you want to do it I can help, otherwise I'll tackle it later.

[trollodel]

I believe this doesn't cover enough cases, as it's not checking the inheritance tree of the inner class itself (only for the outermost class). So the proper way would be to check the inherited constants of the current class, then go the outer one and do the same, then the outer one from that and so on. It's complicated but it should solve all cases.

Yeah, I suspected that (see the note in the OP).

If you want to do it I can help, otherwise I'll tackle it later.

I can work on it, but not in the near future. The idea I had is to have this completed and then work on the other cases in another PR, but I understand why you may want to fix all the cases here.

[trollodel]

Superseded by #69587.