@httpPayload-bound constrained shapes don't work in the server

[david-perez]

Internal tracking: P73926463

(Somewhat) minimal reproducer:

$version: "2.0"

namespace com.amazonaws.simple

use aws.protocols#restJson1
use smithy.framework#ValidationException

@restJson1
service SimpleService {
    operations: [
        Dummy
    ]
}

@http(code: 200, method: "PUT", uri: "/dummy")
operation Dummy {
    input: Dummy_Input
    output: Dummy_Output
    errors: [ValidationException]
}

@input
structure Dummy_Input {
    @required
    @httpPayload
    template: Fancy,
}

@output
structure Dummy_Output {
}

enum ThisOrThat {
    This
    That
}

structure Fancy {
    this_or_that: ThisOrThat
}

Produces:

pub fn deser_structure_crate_model_fancy_payload(
    input: &[u8],
) -> Result<crate::model::Fancy, aws_smithy_json::deserialize::error::DeserializeError> {
    let mut tokens_owned =
        aws_smithy_json::deserialize::json_token_iter(crate::json_deser::or_empty_doc(input))
            .peekable();
    let tokens = &mut tokens_owned;
    let result = crate::json_deser::deser_structure_crate_model_fancy(tokens)?.ok_or_else(|| {
        aws_smithy_json::deserialize::error::DeserializeError::custom(
            "expected payload member value",
        )
    });
    if tokens.next().is_some() {
        return Err(
            aws_smithy_json::deserialize::error::DeserializeError::custom(
                "found more JSON tokens after completing parsing",
            ),
        );
    }
    result
}

Which causes:

error[E0308]: mismatched types
  --> simple/src/json_deser.rs:70:5
   |
53 | ) -> Result<crate::model::Fancy, aws_smithy_json::deserialize::error::DeserializeError> {
   |      ---------------------------------------------------------------------------------- expected `Result<Fancy, DeserializeError>` because of return type
...
70 |     result
   |     ^^^^^^ expected struct `Fancy`, found struct `Builder`
   |
   = note: expected enum `Result<Fancy, _>`
              found enum `Result<fancy::Builder, _>`