Implement logprob for SpecifyShape

[ricardoV94]

Similar to the Dimshuffle case, the best is to let canonicalization move SpecifyShape's out of the way (and improve Aesara if there are obvious missing cases), and only apply a logprob rewrite as the last resort.

The logprob rewrite should be pretty simple

def logprob_specify_shape(op, values, inner_rv, *shapes, **kwargs):
  (value,) = values
  # transfer specify_shape from rv to value
  value = at.specify_shape(value, shapes)
  return logprob(inner_rv, value)