Fix native Smithy client retry and retry response errors (#1717)

* Fix retry for native Smithy clients
* Treat `SdkError::ResponseError` as a retryable transient failure
* Rename `ClassifyResponse` to `ClassifyRetry`
* Rename 'policy' to 'classifier' in AWS SDK public API
* Rename `AwsResponseClassifier` to `AwsResponseRetryClassifier`

Co-authored-by: Zelda Hessler <zhessler@amazon.com>