Align @defer v1 implementation with latest proposed spec updates

[jpvajda]

While @defer support work is in flight (#3556), it has been implemented against a now-outdated version of the proposed spec.

This is a placeholder issue for aligning with the latest implementation (graphql-js PR here graphql/graphql-js#3659, spec edits PR here graphql/graphql-spec#742)

[BoD]

See graphql/defer-stream-wg#41

[jpvajda]

See graphql/defer-stream-wg#50