Expose all compilation stats to processOutput callback

[nealfwilliams2]

I think it would be useful for the processOutput callback to have access to the compilation stats as a second parameter.

In my case, I need the output asset map to include all the assets as well as an ordered list of all the entrypoint chunks.

I would be happen to open a PR adding and testing this feature if you agree this would be a valuable feature.

[ztoben]

That seems reasonable. Happy to take a look at any and all PRs!