Implement sealed trait analysis and expose it in the adapter.

[obi1kenobi]

Make it possible to execute queries like:

{
    Crate {
        item {
            ... on Trait {
                name @output
                sealed @output
            }
        }
    }
}

Under the hood, the sealed property on the Trait vertex type does a fair bit of computation to determine whether the trait is sealed in a variety of ways.