Validation error message for @input / @output seems to be backwards

[rafial]

Given this:

/// Lookup for a particular ASIN if a product is eligible for subscribe and save.
@readonly
@http(uri: "/subscriptions/products/{asin}" method: "GET")
operation IsProductEligible {
    input: IsProductEligibleRequest
    output: IsProductEligibleResponse
    errors: [SubscribeAndSaveClientException, SubscribeAndSaveServiceException]
}

@output
structure IsProductEligibleRequest {
    @required
    @httpLabel
    asin: UrlEncodedString
}

...building produces the following validation error:

| /// Lookup for a particular ASIN if a product is eligible for subscribe and sav…
6| @readonly
7| @http(uri: "/subscriptions/products/{asin}" method: "GET")
8| operation IsProductEligible {
 | ^

Operation output cannot target structures marked with the @input trait

...but in fact it is the the other way around, the operation is targeting for input a structure marked with the @output trait.

The message is similarly backwards when trying to use a structure marked as @input as the output for an operation.

[milesziemer]

Thanks for calling this out. Fixed by #1728