Allow free() to be used as Callable

[vnen]

This method is registered in a special way so ClassDB doesn't naturally know about its existence. Here it is hardcoded if any other option fail to check if it is about the "free()" method and, if so, say it exists and return a Callable.

Fix #86706

[akien-mga]

It seems to make the GDScript test suite crash:

https://github.com/godotengine/godot/actions/runs/7557248007/job/20576060316?pr=87294

[vnen]

Yeah, the problem is some things still tries to get the MethodBind, which does not exist for free(). I'll change back the has_method to avoid this issue and add a more localized solution in GDScript.

[dalexeev]

Looks good to me. Probably worth adding a test.

var node := Node.new()
var callable: Callable = node.free
callable.call()
print(node)

node = Node.new()
callable = node["free"]
callable.call()
print(node)

[vnen]

Added a test.

[akien-mga]

Thanks!