Input profile validation requires nodes in the model

[cabanier]

The Meta Quest Controller Pro was released with a bunch of new features.
These features are exposed as buttons so we want to describe them in the json file.

However, because the validation tool requires that each button has a node in the gltf model, we can't add them
We could add dummy nodes to the model but that feels hacky.

Could we change the validation so gamepad buttons have no corresponding nodes?
@toji @felixtrz