Format code with fourmolu

[ttuegel]

This pull request would apply formatting with Fourmolu automatically. This avoids problems with stylish-haskell and it removes the need for us to manually attend to the style guide. I think the advantages of perfectly-consistent formatting for readability and code review outweigh the disadvantage that the code will sometimes be formatted differently than we would have chosen ourselves.

Fixes #2415.

---

Review checklist

The author performs the actions on the checklist. The reviewer evaluates the work and checks the boxes as they are completed.

• Summary. Write a summary of the changes. Explain what you did to fix the issue, and why you did it. Present the changes in a logical order. Instead of writing a summary in the pull request, you may push a clean Git history.
• Documentation. Write documentation for new functions. Update documentation for functions that changed, or complete documentation where it is missing.
• Tests. Write unit tests for every change. Write the unit tests that were missing before the changes. Include any examples from the reported issue as integration tests.
• Clean up. The changes are already clean. Clean up anything near the changes that you noticed while working. This does not mean only spatially near the changes, but logically near: any code that interacts with the changes!

[ttuegel]

If we decide to adopt fourmolu, we should remove the separation between "groups" in our import lists, so we can take advantage of automatically managing imports.

[ttuegel]

When this is merged, here is how to resolve conflicts with your pull request branch.

git switch master
git pull upstream  # Replace 'upstream' with however you call kframework/kore.
git log  # Find the commit hash of this pull request after it is merged; it is called '$commit' below.
git switch pr-branch  # Replace 'pr-branch' with the name of your branch.
git merge $commit~1
# Resolve conflicts in the usual way.
git merge $commit  # The only conflicts will be due to formatting.
./scripts/resolve-conflicts.sh pr-branch
git commit
# There may still be some conflicts due to files that were deleted.
# Resolve these conflicts the normal way.
git push  # Push changes to GitHub. They will be reformatted automatically.