Implement @range on short (#2034)

* Extract a ConstrainedNumberGenerator from ConstrainedIntegerGenerator

* Update tests' expectations to assume that we support @range for short

* Add ShortShape to all the key places to get @range support

* Generalize generator tests.

* Add tests for the @range trait on short to our constraints.smithy model.

* Update changelog

* Fix type in constraints.smithy