Upgrade to Smithy 1.28.1 (#2463)

* Upgrade to Smithy 1.28.1

* fix a couple of failing protocol tests

* Adhere to new ValidationException message format

* Add RestJsonMalformed to FailingTest

* Add various fixes

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Co-authored-by: Harry Barber <hlbarber@amazon.co.uk>
Co-authored-by: Harry Barber <106155934+hlbarber@users.noreply.github.com>