Update Metro to 0.84.2

Summary:
Notably, fixes a regression where `metro-config` (and therefore `react-native/metro-config` did not ship types, leaving untyped `metro.config.js`.

https://github.com/facebook/metro/releases/tag/v0.84.2

Changelog:
[General][Changed]: Update Metro to ^0.84.2

Reviewed By: cortinico

Differential Revision: D94901986