build: remove rollup.js dependency

[gpbl]

• Remove the rollup.js dependency from the build stack and rely on multiple tsconfig.json to create the CommonJS and ESM builds.
• Remove unneeded postcss dependencies
• Allow import directly react-day-picker/style.css and react-day-picker/style.module.css
• Using package.json's scripts keep compatibility with existing exports.

Note: this change will remove the minified version, which I hope we don't need to support anymore.