[2020-07-02] Add schema validation to GraphQL.js that enforces @deprecated on nonnull

[benjie]

[ACTION - Ivan] - Add schema validation to GraphQL.js that enforces @deprecated on nonnull

assignee(s): @IvanGoncharov
source: https://github.com/graphql/graphql-wg/blob/master/notes/2020-07-02.md#moving-the-deprecated-directive-on-input-fields-rfc-to-stage-2-15m45m-stephen

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[benjie]

@IvanGoncharov I think you said on the call yesterday that this was complete?