Update ESLint config

[friederbluemle]

A couple of minor updates to the ESLint config:

• Move rules into an overrides section, as these should only be applied to TypeScript files (.ts/.tsx)
• Disable no-undef

The reason for disabling no-undef can be found in the official typescript-eslint docs:

We strongly recommend that you do not use the no-undef lint rule on TypeScript projects. The checks it provides are already provided by TypeScript without the need for configuration - TypeScript just does this significantly better.

[emin93]

Thanks for the changes, looks good.

[mikehardy]

Strange, I would have thought these came in from the community eslint defs, I was just in this area for a different template and there's lots of duplication here (not saying what's best, just that it is)

https://github.com/facebook/react-native/pull/32655/files
https://github.com/facebook/react-native/pull/32644/files

and looks like I should do noshadow on the other template too :)

[friederbluemle]

Sure, if these rules already come in from the community eslint config, then of course we should avoid the duplication here. In that case we probably also don't need #238 and we can revert both PRs. I remember in one project I worked on recently, I did need these overrides here, but maybe it was referencing an older version of eslint-config-react-native-community (?) @mikehardy Can you please confirm?