spack: super-fast bundler

[kdy1]

It's far from complete, but I'm opening the pr to use it as a pointer.

Impl notes

• rollup.js does not touch requires and dynamic imports
• webpack can transform both dynamic imports and requires

Tasks

• Minifier (Minifier #826)

• JS interop

  • js loader
  • js resolver

Other APIs including plugin are postponed.

• ES6 import

  • normal import
  • aliased import
  • namespaced import
    • de-globing (& tree shaking)
    • namespaced import with dynamic key

• Dead code elimination (+ tree shaking)

• Chunking

• Correct execution order

  • import statements
  • dynamic imports

• Dynamic imports

  • Loading

• Optimize helpers (remove duplicate)

• .swcrc integration

• "esnext" in package.json

• spack.config.js

• Merging of SourceFile

We also need a way to provide config while testing.

• neon integration

TODOs (postponed)

• common js import (require)
  • Execution order
  • Loading
  • Optional dependency

Ideas

constant optimizations

We can move all pure constants to top level function.
If those are marked with correct hygiene id,
it will be resolved differently and can be removed by minifier.

Fixture tests

  # Stores input files  
  - /input
    # Entries (this includes entry.js)
    - /input/entry*
  # Stores reference outputs
  - /output
    # Output entries
    - /output/entry*
    # Shared modules.
    - /output/chunk*

Closes #681.
Closes #43.