Support eslint 8+ flat plugin syntax out of the box for eslint-plugin-react-compiler

[orta]

Summary

The current docs for the react compiler eslint plugin is based on integrating with the old-style eslint config format. This is generally fine, but most plugins (and the official docs) are now describing themselves in the new format.

This PR has two changes:

• Update the exports to include a "flat configuration"
• Adds a README change describing how to handle both configs

The solution is semi-based on @guillaumebrunerie's answer in reactwg/react-compiler#25 mixed with reading the source code for eslint-plugin-react-refresh

How did you test this change?

I faked this API in the most recent deploy:

Then used that in my app:

and get myself some compiler messages:

/Users/orta/dev/app/apps/puzzmo.com/src/palette/HoverPopover.tsx
  31:37  error  Hooks must always be called in a consistent order, and may not be called conditionally. See the Rules of Hooks (https://react.dev/warnings/invalid-hook-call-warning)  react-compiler/react-compiler

/Users/orta/dev/app/apps/puzzmo.com/src/components/gameplay/PlayGamePauseOverlay.tsx
   33:7   error  Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)  react-compiler/react-compiler
   35:5   error  Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)  react-compiler/react-compiler

[poteto]

Thanks @orta!