Note: This is a reference implementation. closes #16525

Summary

Integrates the sort-package-json Rust crate into oxfmt to automatically sort package.json files according to npm conventions before passing them to Prettier for final formatting.

Changes

• Added sort-package-json v0.0.1 dependency
• Created package_json_sorter module with sorting logic
• Modified format_by_external_formatter() to detect and sort package.json files
• Added unit tests for sorting functionality

Behavior

✅ package.json files are sorted - Fields reordered according to npm conventions (name, version, description, scripts, dependencies, etc.)

✅ Sorting happens before Prettier - The sorted JSON is then formatted by Prettier for consistent spacing

✅ package-lock.json is NOT sorted - Only files named exactly "package.json" are affected

✅ Other JSON files unaffected - Regular .json files continue to work normally

✅ Error handling - Invalid JSON returns clear error messages

Example

Before:

{
  "version": "1.0.0",
  "dependencies": {
    "lodash": "^4.17.21"
  },
  "name": "my-app",
  "scripts": {
    "test": "echo test"
  }
}

After:

{
  "name": "my-app",
  "version": "1.0.0",
  "scripts": {
    "test": "echo test"
  },
  "dependencies": {
    "lodash": "^4.17.21"
  }
}

Test plan

• Unit tests pass (cargo test -p oxfmt)
• Code formatted (just fmt)
• Clippy passes (cargo clippy -p oxfmt)
• Manual testing confirms sorting works correctly

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