Please verify the following:

• yarn test jest tests pass with new tests, if relevant
• yarn lint eslint checks pass with new code, if relevant
• yarn format:check prettier checks pass with new code, if relevant
• README.md (or relevant documentation) has been updated with your changes
• If this affects functionality there aren't tests for, I manually tested it, including by generating a new app locally if needed (see docs).

Describe your PR

• A discussion in Slack broke out about why does App.tsx pass the hideSplashScreen. The ultimate reason was because in v8 we supported both expo-splash-screen and react-native-bootsplash
• This PR simplifies some of the boilerplate's entry point
• Renames App.tsx -> index.tsx to be more aligned with the React Navigation template of Expo's default app (via yarn create expo my-app --template react-navigation/template)