Mock resolvers ignore abstract types

[ling1726]

Repro with instructions and comparison with the relay mock payload generator: https://github.com/ling1726/graphitation-payload-generator-repro

When abstract types are used with the payload generator for @graphitation/graphql-js-operation-payload-generator - they are ignored in favour of concrete types. This makes it hard to create mocks for queries that involve abstract interfaces and polymorphism

[alloy]

To elaborate, the issue is that when we have mocks for interfaces, but the executor is following schema that is referring to concrete types, those interface mocks never get used. For each concrete type, we should check if there are mocks for any of the interfaces that the type implements.