Fix React examples build from fresh checkout

[johnsmith507]

Summary

Fixes #658 by making the React examples usable from a fresh monorepo checkout.

• Resolve local @better-scroll/* packages to their source files for the React example app.
• Compile those local TypeScript package sources through ts-loader instead of requiring prebuilt dist/ artifacts.
• Pin Webpack 4.47.0 so the React example build works on current Node/OpenSSL versions.
• Document how to run and build the React examples.

Verification

• yarn install --ignore-scripts
• yarn react:build