Remove internal enum values from validation message

[srchase]

The enum validation protocol tests were updated in smithy-lang/smithy#1658 to remove enum values with the @internal trait, or which have been tagged with internal. For Smithy IDL 1.0 models which must use the @enum trait (a proper enum shape was introduced with IDL 2.0), the only option for marking an enum value as internal is to use the "internal" tag. For IDL 2.0 models, the preferred way is to use an enum shape, and apply the @internal trait. When Smithy upgrades an enum trait to an enum shape, or downgrades an enum shape to an enum trait, the tags are copied, including an internal tag, but the downgrade does not retain the @internal trait since it cannot be applied to the @enum trait.

For example:

enum Fruit {
    APPLE
    BANANA
    
    @internal
    DURIAN

    @tags(["internal"])
    PAPAYA
}

Validation for the above Fruit enum will check that input is any of the four enum values, but the validation message returned will only include the non-internal values, apple and banana. The same is applied for models which have non-synthetic enum traits, which have not been upgrade to enum shapes.

When https://github.com/aws/aws-sdk-js-v3 updates to use the smithy release that contains smithy-lang/smithy#1658, a PR will be cut to update the generated validation tests.

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[gosar]

In smithy-typescript, the code generator does not convert all enum traits to enum shapes, so we have to check the EnumTrait like before.

[srchase]

Fixed in dc90a62.