[llvm] change contents of ScalarEvolution from private to protected (PR #83052)

[Joshua Ferguson via llvm-commits]

skewballfox wrote:

I wasn't sure if you meant for me to integrate the flag into the existing code like the ScalarPredicate or NoWrap flags, so I added one directly to ScalarEvolution. I'll start pushing after each method. If at any point I need to change something about the implementation, let me know

https://github.com/llvm/llvm-project/pull/83052