Keep track of not loaded files for cabal

[soulomoon]

The main use case:
When we fail to load some files $X$, we know exctaly what files $Y$ we actually did try to load. Where $Y \in X$.

$Y>1$ only make sense if we are using cabal's multiple home unit repl features.

We need this to reduce the number of files we put into senquential loading loop once batch load is failed for haskell/haskell-language-server#4445

TODO:

• The logic is simple, but I think we should add a test for case $Y > 1$. But I don't know how to trigger such loading errors.

[soulomoon]

The basic idea is that we can include new files to be loaded along with old files into LoadWithContext.
If we fail to load them togather, emit the CradleError with the actual files we did call cabal with.
Tests failing-cabal-multi-repl-with-shrink-error-files added, now the patch ready to be reviewed @fendor

[fendor]

Thanks for the PR!
I have a couple of comments and improvements, but otherwise I think this is good to go!

[soulomoon]

cc @fendor , I've addressed the comments, please take a look

[fendor]

LGTM, thanks! One nitpick comment, once you have decided whether you agree or not, you should be able to press the merge button :)