UPSTREAM: 54701: Refactor reconcileAutoscaler method in hpa

There have been a couple of recent bugs in the "normalizing" part of the
`reconcileAutoscaler` method. This part of the code base is responsible
for, among other things, taking the suggested desired replicas based on
the metrics, ensuring it conforms to certain conditions, and updating it
if it does not. Isolate the part that converts the desired replicas
based on a given set of rules into its own function.

We are refactoring this part of the code base to make the logic simpler
and to make it easier to write unit tests.

Author: mattjmcnaughton