rspack/webpack: Backport input source map support to v2 #564

Describe the feature

#562 exposed the input source map for rspack and webpack, making it possible to chain source maps generated by earlier loaders correctly. That PR was written against the v3 branch, which has dropped support for CommonJS builds. This makes the 3.x release branch difficult to adopt at Datadog, so it would be helpful to make this API available on 2.x as well.

Additional information

• Would you be willing to help implement this feature?