[llvm] [IR] Add sparse instruction change printing (PR #221519)

[Alexis Engelke via llvm-commits]

https://github.com/aengelke commented:

This is again quite a lot of code for an internal debugging facility. I'm wondering whether there are easier ways to achieve the same goal. E.g. we have instnamer that could be run before a pass and a later diff should be less noisy then.

https://github.com/llvm/llvm-project/pull/221519