Clean up built-in types

[ttuegel]

Continuation of #2209.

• Pull the built-in primitive types out of Builtin:
  • Kore.Internal.InternalInt
  • Kore.Internal.InternalBool
  • Kore.Internal.InternalString
• Split up the simplification routines for each type.
• Reduce some duplication in the unification code.
• Add missing test cases for unification.
• Update test output. The changes should only be to comments.

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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]

@ana-pantilie I addressed you comments, could you please take another look?

[ana-pantilie]

Looks good to me. I added a commit with some test cases (it used to be a TODO).

[ttuegel]

@ana-pantilie Oh, I added the same sort of tests at Test.Kore.Builtin.{Bool,String}.test_contradiction. I will consolidate them.

[ana-pantilie]

@ttuegel Sorry, I saw the TODO and thought I could add them quickly, it probably just means the TODO was out of date. You can just revert the commit if you think they're redundant and it's easier that way.