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

[William Moses via llvm-commits]

wsmoses wrote:

Being slightly lazy and looking up an old PR which did related things, maybe https://github.com/llvm/llvm-project/commit/99d2582164c4bc8f10c3e3c20dd3690243ad49ba#diff-1e66dd3ceb17c18388ad57f6e7a16e77a836ab1420975572a95b66727a529299 is a good starting point

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