duplicate keys across safe and unsafe params does not fail validation

[bavardage]

What happened?

I am able to produce an error definition with the same param name used both in unsafe-args and safe-args.

Conjure-java then happily produces non-compiling java code:

public static ServiceException myError(
            Throwable cause, int param, List<String> param) {
        return new ServiceException(
                MY_ERROR,
                cause,
                SafeArg.of("param", param),
                UnsafeArg.of("param", param));
    }

What did you want to happen?

I feel like the IR validation should protect against this.

I'm not sure whether it would be enough to change the .toSet() here to a .toList(): https://github.com/palantir/conjure/blob/master/conjure-core/src/main/java/com/palantir/conjure/defs/validator/ErrorDefinitionValidator.java#L34 (and change the unique names validator to take a Collection<>)?