Adds support for useBackgroundQuery and useReadQuery in Streaming SSR

[alessbell]

This PR creates a new class, NextSSRApolloClient in package/src/ssr/NextSSRApolloClient.tsx, which can be imported and used in client components where one would use ApolloClient outside of the app directory.

This extension of the ApolloClient class registers "background queries" (queries triggered by components rendering on the server) via the same registerLateInitializingQueue strategy already used to register results on the client. By keeping track of queries already run on the server, we can avoid duplicating these requests on the client when the same components are executed in the browser, since the result will be streamed in once it has completed.

[alessbell]

I'll add this back - I temporarily removed it for testing with useBackgroundQuery where using a Suspense boundary directly was preferred

[phryneas]

Reminder to add this back :)

[phryneas]

Already some feedback. I'm curious why that deduplication change didn't do what we expected, though. Gonna look a little deeper 👀

[phryneas]

@alessbell I found out what was going wrong.

For type safety, we need a getQuerymanager(this) method returning a typed QueryManager<TCacheShape> instance instead of just accessing this['QueryManager'] everywhere, as that one is any, not QueryManager<TCacheShape>.

Add that and you'll immediately notice ;)

[alessbell]

Thanks for the review, @phryneas! I believe I've gotten to all the feedback (including offline comment re: test helpers addressed in 037c8ba) and I've done some more manual testing. This is ready for a final look :)

[phryneas]

This looks very good!
Only some minor little changes, then this should be good to go!