Summary:
Fixes broken ios/android e2e tests for CI.
Changes:
1. Use `npm pack` instead of `yarn pack` during e2e test
2. Update test string assertions in ios/android e2e tests
3. Use `Step One` as candidate for source code replacement to test for page changes (since the "Welcome to React Native" string exists in the `Header` component instead of being on `App.js`)
## Changelog
[Internal] [Fixed] - Fix ios/android e2e tests
Pull Request resolved: https://github.com/facebook/react-native/pull/24974
Differential Revision: D15431539
Pulled By: cpojer
fbshipit-source-id: 054af2c2fff6bbdb2263c15d7f5cd416aaa507fd