ENH: implement JAX modified Bessel function via exponentially modified version about pytensor

[ricardoV94]

There are two things. We can easily add an ive helper to pytensor.tensor without implementing new Ops

Separately from that, if you want to use iv in JAX we can use the (tfp) ive in the JAX dispatch of iv. Only issue is we need to add tensorflow probability as an (optional) dependency? Also I haven't tried to use it with JAX, so I don't know exactly how the two can me married.

I believe @ColCarroll might have some pointers?

[fonnesbeck]

Another big one we are missing is the error function erfc which keeps us from using the normal CDF in any JAX sampling. There's no JAX implementation either, so we could go the TF route there too.

[twiecki]

Couldn't we copy it over from tfp?