Add FileReader to eslint globals (#30766)

Summary:
Fix eslint complaining about FileReader not being defined.

## Changelog

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[Internal] [Fixed] - Fix eslint complaining about FileReader not being defined.

Pull Request resolved: https://github.com/facebook/react-native/pull/30766

Reviewed By: TheSavior

Differential Revision: D26318564

Pulled By: PeteTheHeat

fbshipit-source-id: d08c040f872cca3cbb26e8bf753a1acb3931d294

packages/eslint-config-react-native-community/index.js

@@ -96,6 +96,7 @@ module.exports = {
     EventTarget: false,
     exports: false,
     fetch: false,
+    FileReader: false,
     FormData: false,
     global: false,
     Headers: false,