Find generating function
與 .wl 參考的差異： `FindGeneratingFunction` is unimplemented
FindGeneratingFunction[{a0, a1, …}, x]
FindGeneratingFunction[{{n0, a0}, {n1, a1}, …}, x]
- FunctionSpace — default Automatic
- Method — default Automatic
- TimeConstraint — default 10
- ValidationLength — default Automatic