[graphiql] Support the proposed "incremental: ..." response format

[rmosolgo]

Hi! I'm trying to use GraphiQL with @defer. I found that it has some support built in via enableIncrementalDelivery, which defaults to true.

However, there's a long-running proposal to change the standard response structure: graphql/graphql-spec#742 .In that proposal, each patch would include a { incremental: [ ... ] } array which includes { data: ... , path: ... } entries.

Although it's only a proposal, it was implemented in GraphQL-JS about a year ago (graphql/graphql-js#3659) and has also been added to urql and apollo client

It looks like GraphiQL expects data and path to be top-level keys in the server's response:

graphiql/packages/graphiql-react/src/execution.tsx

Lines 218 to 219 in 7daa163

	// We pull out errors here, so we dont include it later
	const { path, data, errors, ...rest } = part;

What do you think about also checking for incremental: ... entries there, to support this new response format?

Thanks!

[acao]

our implementation should be updated with whatever the language spec you linked to, and in addition, whatever the graphql over http spec supports! please feel free to open a PR if you like!