Missing and/or empty Query

When:
- no `Query` is defined in the GQL schema, deployment fails with error `There is no top level schema object defined.`
AppSync does not pickup the `Mutation`, nor `Subscription` operations without the `Query` operation being present as well.
- the GQL `schema` is explicitly defined without the `Query` operation, deployment fails with error `A schema MUST have a 'query' operation defined.`
- the GQL `schema` is explicitly defined with empty `Query` operation, then the „Queries“ page in AppSync API console fails to load

### Bugs reproduction
All 3 scenarios are demonstrated in this bug reproduction here: [https://github.com/testuj-to/appsync-missing-query](https://github.com/testuj-to/appsync-missing-query)

Start with the reproduction repository linked in the issue and run its three schema scenarios: no Query, an explicitly defined schema without Query, and an empty Query. Compare the deployment and AppSync console failures in each case, then establish the expected handling for missing or empty Query operations; completion should address all three reproduced cases.

Written by the indexing model from the issue text.