Validate fiscal number when exists, require for AstroPay

Add basic checks for a valid format when it's present,
and require it for AstroPay. Does not calculate check digits.
Removes punctuation for validation, and on staging for processors
that want to receive it without separators.

Bug: T106171
Change-Id: If4640367b84edcb8cfb3900c0ca79ede7450b03d