[SCEV] Support ule/sle exit counts via widening (#92206)

If we have an exit condition of the form IV <= Limit, we will first try
to convert it into IV < Limit+1 or IV-1 < Limit based on range info (in
icmp simplification). If that fails, we try to convert it to IV < Limit
+ 1 based on controlling exits in non-infinite loops.

However, if all else fails, we can still determine the exit count by
rewriting to ext(IV) < ext(Limit) + 1, where the zero/sign extension
ensures that the addition does not overflow.

Proof: https://alive2.llvm.org/ce/z/iR-iYd