Use deno internal code to generate main bundle

[kitsonk]

In #2490 it was discussed that depending on code in deno_std as part of Deno is "problematic" because we can't easily get rollup to support extensioned TypeScript. With the deno bundle feature landing, we could in theory for most/all of our internal code bundles use Deno itself to generate its own bundles.

There are a couple considerations:

• currently bundle source maps aren't parsed out and made available inside Deno. This is talked about in Bundling V2 #2475, but we don't have this yet. We would want that to see where in the bundle internal code "broke" or participated in a stack trace.
• we would have to embed a bundle loader into the bundle/snapshot.

[kitsonk]

For future generations, the need to generate a bundle was removed from the build process, versus actually generating it using the bundling capability of Deno.