function get_rune(node, scope) {
	if (!node) return null;
	if (node.type !== 'CallExpression') return null;

	const keypath = get_global_keypath(node.callee, scope);

	if (!keypath || !is_rune(keypath)) return null;
	return keypath;
}
Returns the name of the rune if the given expression is a `CallExpression` using a rune.
@param {Node | null | undefined} node
@param {Scope} scope