@GraphQLInterface does not find implementations if implementations never used

[ayhanap]

Given the following testCase https://gist.github.com/ayhanap/e4fcf72591fe960db658f6f1967447e2 @GraphQLInterface annotation does not search for its implementations. So if we have a field with method resolver returning an interface, it cannot resolve types because they are never being registered at GraphQLSchemaDfsTraversal.createGraphQLObjectTypeRecursively(...). Because types never used are not registered at all.