[InstCombine] Fold BW/2+1 tops bits are same pattern

Match "icmp eq (trunc (lsr A, BW), (ashr (trunc A), BW-1))", which checks
the top BW/2 + 1 bits are all the same. Create "A >=s INT_MIN && A <=s
INT_MAX", which we generate as "icmp ult (add A, 2^BW-1), 2^BW" to skip
a few steps of instcombining.
https://alive2.llvm.org/ce/z/NjH6Ty
https://alive2.llvm.org/ce/z/_fEQ9P

Differential Revision: https://reviews.llvm.org/D109155