A validation idea from @bbakerman

Because type wiring is registered by string name, we allow a data fetcher registration to a field in an interface type because as the time of pre schema building, we don't know its an interface. I guess with more work we could "validate" this once we have the real schema in place and we know all the types

Investigate if we can validate that datafetchers are only wired on concrete types

Potential idea

allow RuntimeWiring building as we have it day (since we have no schema elements yet)
then at "schema generation time" we validate that the values in the graphql.schema.GraphQLCodeRegistry make sense
eg data fetchers only on fields of a concrete type
type resolvers ONLY on non concrete type
all non concrete types have a type resolver
etc...