eslint 9+ with flat config support.

[itsmnthn]

There has been new version of ESLint v9 that ships with new flat config.

[jefflee-figma]

This plugin relies on typescript-eslint, which doesn't support ESLint 9 yet. There is an open issue for this in the typescript-eslint repo. Once typescript-eslint has stable support for the new eslint version, we can look into upgrading our instructions. For the time being, we'll update the README to denote the temporary incompatibility with ESLint 9.

[jefflee-figma]

Update: now we're waiting for typescript-eslint 8 to be released.