Avoid need for wrapper around single argument GraphQL input types with Querydsl and Query By Example

[rstoyanchev]

Currently, QueryByExampleDataFetcher creates the example Object from the full arguments map. For queries with a single argument that is a GraphQL input type, this means the example object isn't the direct equivalent of the GraphQL input type, but rather a wrapper around it with the GraphQL input type as its only field.

We can improve this by detecting that a query has a single argument that is a GraphQL input type, and have the QueryByExampleDataFetcher use that argument as its source rather than the full arguments map.

The same applies to QuerydslDataFetcher, which builds a predicate relative to the full map, but for such single argument queries, it might make more sense to nest and be relative to that argument.

[rstoyanchev]

It looks like we may be able to look this up at runtime via getFieldDefinition().getArguments() on DataFetchingEnvironment, which would work transparently for both auto-registered and manually registered DataFetcher repositories.

If that doesn't work, we could try getFieldDefinition().getInputValueDefinitions() on FieldWiringEnvironment from the WiringFactory in AutoRegistrationRuntimeWiringConfigurer, but that would only cover auto-registrations. For manually registered ones, one would have to provide the argument name.