Fix mislabelled polyfills for Object.entries and Object.values (#31880)

Summary:
The polyfills for `Object.entries` and `Object.values` are in a file named `Object.es7.js` when these APIs form part of ES8/ES2017 (https://en.wikipedia.org/wiki/ECMAScript#8th_Edition_–_ECMAScript_2017).

The docs (https://reactnative.dev/docs/javascript-environment#polyfills) list these correctly as ES8 so I thought it might reduce confusion if anyone starts looking into the polyfills in the future like I did.

## Changelog

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[Internal] [Fixed] - Fix filename to include correct ECMA spec

Pull Request resolved: https://github.com/facebook/react-native/pull/31880

Test Plan: All unit tests pass.

Reviewed By: yungsters

Differential Revision: D29820165

Pulled By: ShikaSD

fbshipit-source-id: 2a4eb58bed7b7a4089406665c5c9115cb1773ff6