[Bug]: Packages created with `create-rslib` fail to build in Webpack 4 projects

[Colin3191]

Version

System:
    OS: Windows 11 10.0.26100
    CPU: (16) x64 12th Gen Intel(R) Core(TM) i5-12600KF
    Memory: 18.99 GB / 31.83 GB
  Browsers:
    Edge: Chromium (130.0.2849.46)
    Internet Explorer: 11.0.26100.1882

Details

When using an npm package generated by create-rslib in a Webpack 4 project, the build fails with module resolution errors. This occurs because:

1. The generated package.json only contains the exports field
2. Webpack 4 has limited support for the exports field resolution
3. Missing fallback main/module fields that Webpack 4 expects

Reproduce link

N/A

Reproduce Steps

1. Create a package using create-rslib
2. Use it in a Webpack 4 project
3. Run build command
4. Observe module resolution failure

[fi3ework]

webpack 4 is already quite outdated. We prefer that newly created packages adopt future-proof configurations, as the vast majority of bundlers recognize the exports field. Scenarios where it's not recognized are, in my opinion, less than 5%. Excessive configuration can also increase the burden of maintaining package.json.