Missing rational function simplifications

[brandonwillard]

We're missing some simplifications for rational functions. For example:

import aesara
import aesara.tensor as at


eta_at = at.scalar("eta")
kappa_at = at.scalar("kappa")

# This is equivalent to `1 / kappa_at`
graph_at = eta_at / kappa_at + (1 - eta_at) / kappa_at

graph_fn = aesara.function([eta_at, kappa_at], graph_at)

# The "optimized" graph still contains the unnecessary `eta` parameter:
aesara.dprint(graph_fn.maker.fgraph)
# Elemwise{Composite{((i0 / i1) + ((i2 - i0) / i1))}} [id A] ''   0
#  |eta [id B]
#  |kappa [id C]
#  |TensorConstant{1.0} [id D]