[llvm] [SCEV] Prove predicate via nuw AddRec value at max iteration (PR #210844)

[Abhay Kanhere via llvm-commits]

AbhayKanhere wrote:

Widened the trip count computation to ensure trip count computation does not overflow, also using loop guards and willNotOverflow checks. 
The negative tests added will need to be modified once https://github.com/llvm/llvm-project/pull/210784 merges. 

https://github.com/llvm/llvm-project/pull/210844