feat(bundle-source): Add JSON cache mode

[kriskowal]

• Adds a --cache-json mode that:
  • Generates .json bundle files in JSON format.
  • Generates -json-meta.json meta files in JSON format.
• Adds a --cache-js mode that should replace --to:
  • Generates .js bundle files in JSON format.
    Adds a UNIX newline absent when using --to.
  • Generates -json-meta.json meta files in JSON format instead of
    -meta.js.

[dckc]

yes, let's