[SCEV] Use SCEVPtrToAddr instead of SCEVPtrToInt in SCEV. (#180244)

Use SCEVPtrToAddr instead of SCEVPtrToInt for pointer -> int
conversion in SCEV, like when computing trip count expressions.

getPtrToIntExpr now also creates SCEVPtrToAddrExpr.

Removal of SCEVPtrToIntExpr out of this PR, to limit the scope and
will be done as NFC follow-up.

PR: https://github.com/llvm/llvm-project/pull/180244
GitOrigin-RevId: 8e76c3f0d29a713c41f1b3d0f19d965a504481cf