Add validation and codegen for custom validation exception traits

[jasgin]

Motivation and Context

Adds ability to define custom validation exceptions per RFC:

• https://github.com/smithy-lang/smithy-rs/blob/custom-validation-rfc/design/src/rfcs/rfc0047_custom_validation.md

Description

Adds ability to use the following traits:

• @validationException
• @validationMessage
• @validationFieldList
• @validationFieldName
• @validationFieldMessage

to define a custom validation exception for a service or operation.

Updated Smithy validation ensures:

• The custom validation exception shape also has @error trait
• The custom validation exception shape has exactly one member with the @validationMessage trait
• Default constructibility if it contains constrained shapes
• At most one custom validation exception is defined
• smithy.framework#ValidationException is not used in an operation or service is a custom validation exception is defined
• Operations with constrained input have exactly one of the default validation exception or a custom validation exception attached to their errors.

Testing

• For unit testing, the following were added/updated:
  • codegen-server-traits/src/test/kotlin/software/amazon/smithy/rust/codegen/server/traits/ValidationExceptionTraitTest.kt
  • codegen-server-traits/src/test/kotlin/software/amazon/smithy/rust/codegen/server/traits/ValidationMessageTraitTest.kt
  • codegen-server-traits/src/test/kotlin/software/amazon/smithy/rust/codegen/server/traits/ValidationFieldListTraitTest.kt
  • codegen-server-traits/src/test/kotlin/software/amazon/smithy/rust/codegen/server/traits/ValidationFieldNameTraitTest.kt
  • codegen-server-traits/src/test/kotlin/software/amazon/smithy/rust/codegen/server/traits/ValidationFieldMessageTraitTest.kt
  • codegen-server/src/test/kotlin/software/amazon/smithy/rust/codegen/server/smithy/ValidateUnsupportedConstraintsAreNotUsedTest.kt
  • codegen-server/src/test/kotlin/software/amazon/smithy/rust/codegen/server/smithy/customizations/CustomValidationExceptionDecoratorTest.kt
  • codegen-server/src/test/kotlin/software/amazon/smithy/rust/codegen/server/smithy/validators/CustomValidationExceptionValidatorTest.kt
• For integration testing
  • serverIntegrationTests in codegen-server/src/test/kotlin/software/amazon/smithy/rust/codegen/server/smithy/customizations/CustomValidationExceptionDecoratorTest.kt
• For e2e integration testing
  • codegen-server-test/custom-test-models/custom-validation-exception.smithy
  • codegen-server-test/build.gradle.kts
• For regression testing
  • The existing e2e integration tests in codegen-server-tests use common models in codegen-core/common-test-models, which use the default smithy.framework#ValidationException

Ran with export RUSTFLAGS="-D warnings -A clippy::redundant_closure -A non_local_definitions" until fixed in server runtime crates. See #4122.

Checklist

• For changes to the smithy-rs codegen or runtime crates, I have created a changelog entry Markdown file in the .changelog directory, specifying "client," "server," or both in the applies_to key.
• For changes to the AWS SDK, generated SDK code, or SDK runtime crates, I have created a changelog entry Markdown file in the .changelog directory, specifying "aws-sdk-rust" in the applies_to key.

---

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[rcoh]

we can decide if we want another pass on the codegen stuff. otherwise looks fine

[drganjoo]

This prevents unused custom validation exceptions in the Smithy model. For example, this model:

use smithy.framework#ValidationException
use smithy.rust.codegen.traits#validationException

@title("Sample Service")
service BurgerService {
    version: "2024-03-18"
    operations: [
        EatBurger,
    ]
}


@http(uri: "/eat/{name}", method: "POST")
operation EatBurger {
     input := @sensitive {
        @required
        @httpLabel
        name: String

        @required
        @httpHeader("size")
        size: String
    }
    output := {
        @required
        value: Integer
    }
    errors: [
        ValidationException
    ]
}

@validationException
@error("client")
structure BurgerValidationException {
    message: String
}
```

generates this error:

```bash
Caused by: ValidationResult(shouldAbort=true, messages=[LogMessage(level=SEVERE, message=Operation com.test#StreamBurgerOrders uses the default ValidationException, but a custom validation exception is defined.
Remove ValidationException from the operation's errors and use the custom validation exception instead.
For documentation, see https://smithy-lang.github.io/smithy-rs/design/server/validation_exceptions.html), LogMessage(level=SEVERE, message=Operation com.test#EatBurger uses the default ValidationException, but a custom validation exception is defined.
Remove ValidationException from the operation's errors and use the custom validation exception instead.
For documentation, see https://smithy-lang.github.io/smithy-rs/design/server/validation_exceptions.html)])
        at software.amazon.smithy.rust.codegen.server.smithy.ValidateUnsupportedConstraintsKt.validateModelHasAtMostOneValidationException(ValidateUnsupportedConstraints.kt:354)
        at software.amazon.smithy.rust.codegen.server.smithy.ServerCodegenVisitor.execute(ServerCodegenVisitor.kt:241)
        ... 16 more

[ysaito1001]

Only reviewed codegen-core, codegen-traits.