fix(webpack-config): fix import export treeshaking

[EvanBacon]

Why

• Fix regression introduced in 🌲 Reduce bundle size on Web by 80% software-mansion/react-native-reanimated#3278
• Alternative to Add @babel/plugin-proposal-export-namespace-from in metro-react-native-babel-preset facebook/metro#760

How

• Enable tree shaking feature https://webpack.js.org/configuration/optimization/#optimizationusedexports
• Not sure if this will have other repercussions.

Test Plan

• EXPO_BETA=1 yarn create expo-app -t tabs
• yarn expo install react-native-reanimated
• This won't fail when using the proposed changes.