Support configurable chunk path prefix

[ggoodman]

Given a configuration like this:

{
  bundle: true,
  entrypoints: ['./src/A/index.ts', './src/B/index.ts'],
  format: 'esm',
  outdir: './dist',
  outbase: './src',
  splitting: true,
}

The resulting build might look like this:

dist
  A
    index.js
  B
    index.js
  chunk.1.js
  chunk.2.js

If a package.json is put in that directory and it is used as the basis of producing an npm module called my-module, tooling like the TypeScript language server will complete import {} from 'my-module/ with a dialogue showing all of the chunks intermingle with the legitimate sub-packages (at least until it starts respecting the "exports" field in the package.json).

It would be helpful to have a measure of control over where the chunks get placed to prevent them from polluting completion in this way. It's a minor thing but perhaps a bit of feedback that might be helpful in your planned code-splitting refactor.

[evanw]

Closing as a duplicate of #553 and #187.

[evanw]

FYI this is being implemented ahead of #553. See #888 and the release notes for more information.