docs: Add information about Expo and usage with Expo and Next.js

[amandeepmittal]

Why

Currently, the styled-components docs do not have any information about Expo.

How

This PR

• fixes/updates snack link in React Native section to use snack.expo.dev instead of legacy snack.expo.io
• adds a new section about Expo after React Native.
• adds a sub section about usage with Expo and Next.js (what configuration is required to set up to use styled-components in project that uses both Expo and Next.js)
• adds a sub-section about tree-shaking and info about large bundle size

Test plan

• Run docs locally using yarn dev
• Visit http://localhost:3000/docs/basics#expo to see the changes
• Run yarn test -u