Bump Node 18 -> 20 to build React Native in OSS (#49658)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/49658

This bumps the version of Node that we use to build React Native from 18 to 20.
We'll still be supporting building with 20, but we'll moving our toolchain to Node 20 becuase 18 is at EOL soon.

Changelog:
[General] [Changed] - Bump Node 18 -> 20 to build React Native in OSS

Reviewed By: javache, cipolleschi

Differential Revision: D70168003

fbshipit-source-id: b64ee583b2d2e72d25393119ae9e9029a74d5b13