webpack: Sourcemap externals when replayed in the browser (#75863)
This was already implemented in the middleware for Turbopack but absent when Webpack was used. We now always prefer the native `findSourceMap` over invoking Webpack's API.
This way stackframes from externals are now properly sourcemapped (and therefore ignore-listed)
Notice how the `react-server-dom-webpack...` stackframe (`console.error` method) wasn't ignore-listed before.
Before:
After:
next.js
ed676009 - webpack: Sourcemap externals when replayed in the browser (#75863)
