Structure:

key = {
	slot = inventory slot type
	# A feature from each of these groups will be assigned automatically on creation
	required_features = { group group group }
	# These feature groups can be added after creation in script
	optional_features = { group group group }
	# optional field with no gameplay effect. Only needed for automatic test artifact generation
	default_visuals = visuals_key
}

The artifact_KEY is also used as a loc key in some contexts. E.G., "artifact_helmet"
