Define a function to return operation shapes that need a `ValidationException` (#3720)

Refactor and define a separate function that returns a set of operation
shapes that must have a supported validation exception shape in their
associated errors list.

This helps identify which type of `ValidationException` has been added
to the operation shape's errors list.

Closes: [3722](https://github.com/smithy-lang/smithy-rs/issues/3722

)

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Co-authored-by: Fahad Zubair <fahadzub@amazon.com>
Co-authored-by: david-perez <d@vidp.dev>