VSCE: Migrate from Webpack to esbuild

Created by: tjkandala

Our VS Code extension's build times are continuously slowing down as we get closer to v1. We find ourselves having to build more and more bundles to support new features (e.g. main extension bundle for web/web worker VS Code and desktop/node VS Code, multiple webview bundles that pull from massive amounts of shared code), which contributes to long build times. To improve developer experience, we should try to migrate to esbuild.

We already have experimental support for esbuild for the web app, with great improvement over Webpack (~3s vs ~53s). We should build off this experimental support as well as add support for production builds.