Add application/config/enable_uids project setting

[dhoverml]

Closes: godotengine/godot-proposals#7195

[AThousandShips]

You haven't registered this class, without doing so it won't work, you need to use GDREGISTER_ABSTRACT_CLASS like is done with ResourceUID

[dhoverml]

Nice catch!
Interesting that I ran into no issues while testing this, though I didn't try using ResourceUID in GDScript.
Wonder if this case should be static_assert at compile time, similar to #81020.
Anyway, I've pushed an update.

[AThousandShips]

The opposite is impossible unfortunately, and there are many valid cases of not registering a class for when they aren't enabled

Edit: To clarify why I say it isn't possible:
With my changes to check at registration there's a well defined point of failure, when the class is registered, but doing the opposite isn't trivial, how do you define the point when a class hasn't been registered? Arguably you could create a solution having some large list of all classes that have been declared, but it'd be very complicated and would probably be hard or impossible to do without making every header file dependent on every other header file

[AThousandShips]

You need to document the method is_dummy, the easiest way to do this is run --doctool on the compiled version of your contribution, see here

[dhoverml]

I was thinking, would it be preferable to modify ResourceUID to always check if the project setting is set (or cache a bool in its constructor)? That way there wouldn't be a new class. Let me know what you prefer.

[AThousandShips]

It shouldn't check the setting every time, that would be too bad performance wise, but it could load the value on creation (as it is only changed on restart) and then use that value

[dhoverml]

Okay, I removed ResourceUIDDummy and instead cache the project setting. Also updated the docs.
Also, maybe _is_dummy should be renamed to is_stubbed, though I don't mind either way.