build: use rollup for better tree-shaking

[pd4d10]

This PR uses rollup instead of webpack to build production bundles:

• [x] ESM bundle (dist/mesh.esm.js): For ES Module with tree-shaking
• [x] UMD bundle (dist/mesh.js): For CommonJS, AMD and global variable pattern
• [x] minified UMD bundle (dist/mesh.min.js): For CDN host

The other npm scripts (such as npm start) are kept as is.