feat: add DevTools hook

[koba04]

Fixes #2003

This adds a DevTools hook to inspect DevTools middleware.
SWR has to expose the React instance to the DevTools to avoid a multiple React instance error in the DevTools middleware.

I've also worked on the DevTools side at koba04/swr-devtools#55

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Latest deployment of this branch, based on commit 9def180:

Sandbox	Source
SWR-Basic	Configuration
SWR-States	Configuration
SWR-Infinite	Configuration
SWR-SSR	Configuration

[shuding]

Perfect, thank you!

[koba04]

Thank you!