Picocli should instantiate `LinkedHashSet` instead of `HashSet` for `Set` fields to preserve input ordering

[remkop]

If an @Option or @Parameters field is null, picocli will instantiate it.

If the Collection type is not a concrete class, picocli will make a best effort to instantiate it based on the field type.

For Set fields, picocli should instantiate LinkedHashSet instead of HashSet to preserve the input ordering.