[llvm] [MachineOutliner][NFC] Refactor (PR #105398)

[Kyungwoo Lee via llvm-commits]

kyulee-com wrote:

> Can you elaborate more in the PR/commit message about why you're making some of these changes? Things like the 2 -> MinRep. Taken as an individual change it would be good to have a rational without depending on future changes to make sense of it.

Yeah. I updated the summary with some details + the link for the next candidate PR.

https://github.com/llvm/llvm-project/pull/105398