function from_fs(str) {
	str = posixify(str);
	if (!str.startsWith('/@fs')) return str;

	str = str.slice(4);
	// Windows/Linux separation - Windows starts with a drive letter, we need to strip the additional / here
	return str[2] === ':' && /[A-Z]/.test(str[1]) ? str.slice(1) : str;
}
Removes `/@fs` prefix from given path and posixifies it
@param {string} str