Revert React 19RC to React 18.3.1 (#47380)

Summary:
While we're waiting for 19 stable, let's bring main back to 18.3.1 ahead of the 0.77 branch cut. We'll land this change just after 19 stable lands.

This is a cherry pick of b93b378fa03e4e85a9e32c651f2f1f6d54033af4 which landed in 0.76 already

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## Changelog:

[INTERNAL] - Revert React 19RC to React 18.3.1

Pull Request resolved: https://github.com/facebook/react-native/pull/47380

Test Plan: CI

Reviewed By: cipolleschi

Differential Revision: D65430775

Pulled By: cortinico

fbshipit-source-id: f0f211754c8ffe5d037fd299e4de52c29d1d7913