Make httpResponseCode be coupled with required

[david-perez]

Currently, this is valid (taken from the restJson1 protocol tests):

@idempotent
@http(uri: "/HttpResponseCode", method: "PUT")
operation HttpResponseCode {
    output: HttpResponseCodeOutput
}

structure HttpResponseCodeOutput {
    @httpResponseCode
    Status: Integer
}

How should a server behave when Status is not provided? The spec does not mention. Should it fall back to 200? In our Rust sSDK implementation, we are currently failing to serialize the response.

I think httpResponseCode without required should not be allowed, since status code cannot be omitted from the HTTP response as per the RFC.

[JordonPhillips]

How should a server behave when Status is not provided?

You use whatever is set on the http trait. I'll double check existing implementations.

[jjant]

@kstich @JordonPhillips regarding the RestJsonHttpResponseCodeDefaultsToModeledCode test, isn't the code missing in the operation's @http trait?

[kstich]

The code value of the @http trait defaults to 200 if not provided