Update Metro to 0.84.0 (#55672)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/55672

Bump Metro minimum to 0.84.0

Although this is a semver-breaking release for Metro, that's only because of the slightly increased Node.js version requirements *already present in React Native*, so this bump is non-breaking for RN.

Full changelogs since previous bump:
https://github.com/facebook/metro/releases/tag/v0.83.4
https://github.com/facebook/metro/releases/tag/v0.84.0

Changelog: [General][Changed] Metro bump to ^0.84.0

Reviewed By: huntie

Differential Revision: D94020063

fbshipit-source-id: 4562517e726b9e2c7d803353ac083fd76a21c261