Implement new navigation mesh callback API

[CodeDoctorDE]

Description

I read the documentation here: https://terrain3d.readthedocs.io/en/stable/docs/navigation.html#baking-a-nav-mesh

and it says that the built in bake button shouldn't be used, because of godotengine/godot-proposals#5138.
This proposal was already implemented. Should this notice be removed?

[TokisanGames]

That PR implemented a new API. We aren't using that API. So, the nav region bake button shouldn't be used until someone implements the callbacks.

[CodeDoctorDE]

Oh okay, thanks for the clarification