summary

Migrates from closure to esbuild/babel/terser for the production builds (amp dist).
The code in this PR is a POC, and there is likely much more cleanup/deletion that we could pursue if we decide to land this.

Changes:

• All builds merge into a single flow. This includes vendor builds, npm binaries, minified, unminified, and esm/es5.
• Enabled terser's mangle property mode, specifically for vars that end with an underscore. This is fairly dangerous, and only works because of two disabled optimizations (compress.properties, mangle.properties.keep_quoted).
  • I also removed comments from terser, not sure why we have them on today.
• I moved build-constant replacement to esbuild, and we can definitely move the rest as well. I don't feel strongly about this and would be happy keeping them all in babel.