What problem does this feature solve?

When using moduleConcatenation:true, the call to compilation.chunkGraph.getChunkModules(chunk) only returns the top level concatenated modules, and there is no way to access the nested modules.

In Webpack, you can access the nested modules with

type ConcatenatedModule {
    ...
    modules: Module[]
}

I saw #6784 exposes this information to the stats plugin. Can we also expose this information to the JS API?

What does the proposed API of configuration look like?

Expose modules property on concatenated modules, which would be a list of the modules that are contained in the ConcatenatedModule