periodic function needs more expandability

[JSS95]

I am making a custom function which has periodicity.
I added period() method to it, which emulate trigonometric function's period() method.

When trigonometric function is passed, periodic function calls period() method of it. I think it would be nice for it to call that method (if exists) for every type of arguments. (Or, maybe a method named _eval_period() can be introduced)

[czgdp1807]

Some work has been in done #18327 (Please Take Over) related to this issue.