Map React.Context instances by React.createContext

[phryneas]

For reference, using React.version as a key caused problems over in react-redux for people who used multiple versions of preact that all report the React version 17.0.2.

Checklist:

• If this PR contains changes to the library itself (not necessary for e.g. docs updates), please include a changeset (see CONTRIBUTING.md)
• If this PR is a new feature, please reference an issue where a consensus about the design was reached (not necessary for small changes)
• Make sure all of the significant new logic is covered by tests (I'd rather not add an integration test with multiple versions of preact)

[changeset-bot]

🦋 Changeset detected

Latest commit: 6084b58

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@apollo/client	Patch

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[github-actions]

size-limit report 📦

Path	Size
dist/apollo-client.min.cjs	37.03 KB (+0.03% 🔺)
import { ApolloClient, InMemoryCache, HttpLink } from "dist/main.cjs"	43.64 KB (+0.03% 🔺)
import { ApolloClient, InMemoryCache, HttpLink } from "dist/index.js"	32.63 KB (0%)
import { ApolloProvider } from "dist/react/index.js"	1.31 KB (+0.76% 🔺)
import { useQuery } from "dist/react/index.js"	4.34 KB (+0.25% 🔺)
import { useLazyQuery } from "dist/react/index.js"	4.66 KB (+0.15% 🔺)
import { useMutation } from "dist/react/index.js"	2.57 KB (+0.31% 🔺)
import { useSubscription } from "dist/react/index.js"	2.32 KB (+0.26% 🔺)
import { useSuspenseQuery } from "dist/react/index.js"	3.7 KB (+0.22% 🔺)
import { useBackgroundQuery } from "dist/react/index.js"	3.91 KB (+0.18% 🔺)
import { useReadQuery } from "dist/react/index.js"	2.64 KB (0%)
import { useFragment } from "dist/react/index.js"	2.12 KB (+0.28% 🔺)

[jerelmiller]

Hopefully this does this trick 🤞