global subscription context config option

[StevenACoffman]

Add global subscription_context_field config option

This is PR for #3863 and is a follow-up to #4230

After #4230, @michelepra revised PR #4191 and added a PR comment that suggested that now the PR should be rebased on top of the implementation merged in #4230

However, that branch hadn't actually been rebased, but instead the latest master had been merged into that branch, and then it appeared that an AI assistant had reconciled any conflicts and made a few other changes. However, the branch had a few problems, and still added more logic and complexity to the templates.

Instead of keeping a separate runtime/codegen path for subscription_context_field, the global config option can > be implemented as a thin opt-in layer over the same logic introduced by #4230:

• @subscriptionContext remains the field-level opt-in.
• subscription_context_field: true enables the same behavior globally for all subscription fields in the analyzed > schema.
• Generated resolvers use the same graphql.Event[T] API introduced by #4230.
• The runtime continues to use the same ResolveFieldStreamWithEventContext, ExecWithEventContext, and subscription response handling already merged upstream.

Signed-off-by: Steve Coffman steve@khanacademy.org

[coveralls]

coverage: 0.0%. remained the same — response_generated_context into master