This test implements the KHR_node_visibility extension and sets the visibility of each node.

Open questions/tasks:

1. Should extension data be saved in each node's info dictionary? Since the extensions list is a dictionary of dictionaries, we may need to squash the two keys to fit into info (something like { "KHR_node_visibility: visibility": "true" })
2. I'm sure there's a better way to iterate through a dictionary_t than what I'm doing here 😅