Implement graphql.schema.LightDataFetcher

[adrian-skybaker]

graphql-java 20.0 introduced the concept of a lightweight data fetcher, to reduce the amount of redundant DataFetchingEnvironment objects wastefully created when just calling simple object properties.

Ideally graphql.kickstart.tools.resolver.TrivialMethodFieldResolverDataFetcher would implement this, to make use of the internal optimisations in graphql-java.

[oryan-block]

Done in #788