[TypePromotion] Extend TypePromotion::isSafeWrap

This modifies the preconditions of TypePromotion's isSafeWrap
method, to allow it to work from all constants from the ICmp.
Using the code:
  %a = add %x, C1
  %c = icmp ult %a, C2

According to Alive, we can prove that is equivalent to
icmp ult (add zext(%x), sext(C1)), zext(C2)  given
C1 <=s 0 and C1 >s C2.
https://alive2.llvm.org/ce/z/CECYZB
Which is similar to what is already present. We can also
prove icmp ult (add zext(%x), sext(C1)), sext(C2) given
C1 <=s 0 and C1 <=s C2.
https://alive2.llvm.org/ce/z/KKgyeL

The PrepareWrappingAdds method was removed, and the
constants are now altered to sext or zext directly as
required by the above methods.

Differential Revision: https://reviews.llvm.org/D113678