Add poisson_binomial lpmf/lcdf/lccdf/rng

[rok-cesnovar]

The following signature recently got stan math support.

real poisson_binomial_lpmf(int, vector)
real poisson_binomial_lpmf(int[], vector)
real poisson_binomial_lpmf(int[], vector[])
real poisson_binomial_lcdf(int, vector)
real poisson_binomial_lcdf(int[], vector)
real poisson_binomial_lcdf(int[], vector[])
real poisson_binomial_lccdf(int, vector)
real poisson_binomial_lccdf(int[], vector)
real poisson_binomial_lccdf(int[], vector[])
int poisson_binomial_rng(vector)

I can handle the stanc3 PR but would require help for the docs PR.

[rok-cesnovar]

This is blocked by missing deprecated suffixes.

[WardBrian]

I believe we can add these without the deprecated suffixes using #1191 and the missing_math_functions list, no?

[rok-cesnovar]

Yes, we can add this now finally.

[WardBrian]

It seems like the deprecated signatures actually were added, its https://github.com/stan-dev/math/issues/2490 which is still blocking