Explore Rolldown as backward-compatible upgrade from Rollup and ESBuild

[eliot-akira]

Rolldown is the next-generation bundler from the authors of Rollup.

• Designed to serve as the underlying bundler in Vite, with the goal to replace esbuild and Rollup with one unified build tool.
• Written in Rust. It is on the same performance level with esbuild and 10~30 times faster than Rollup.
• Supports the same plugin API with Rollup / Vite, ensuring compatibility with Vite's existing ecosystem.