@semanticNonNull and semantic nullability support

[slightlytyler]

What happened?

Currently gqlgen does not support @semanticNonNull directive which is currently proposed as an interim solution to the semantic nullability proposal. To support this I think gqlgen would need to:

• Handle fields marked as @semanticNonNull in codegen. This would mean the codegen types would disallow null values being returned from the resolvers and the runtime would prevent null propagation caused by returning errors.
• Include @semanticNonNull annotations in introspection.

There might be additional details needed for support but these are the ones I was able to identify.

What did you expect?

Minimal graphql.schema and models to reproduce

versions

• go run github.com/99designs/gqlgen version?
• go version?