Support graduating *.Extended modules to override standard modules with mixins

Something I thought to do while refactoring https://github.com/hasura/graphql-engine/pull/3622 but which needs to wait.

See https://stackoverflow.com/questions/59739476/deprecate-or-shadow-a-module-or-function-from-a-third-party-library#59740286

This seems to work pretty well except that it breaks `stack ghci`: https://github.com/commercialhaskell/stack/issues/3862

So I think this is blocked on the work in https://github.com/hasura/graphql-engine/pull/3558