[InstSimplify] Add simplifications for `umin/umax(uadd/usub.sat(X, Y), X)`

[goldstein.w.n]

Summary

umax(uadd.sat(X, Y), X) --> uadd.sat(X, Y)

• https://alive2.llvm.org/ce/z/mEJk_t

umin(uadd.sat(X, Y), X) --> X

• https://alive2.llvm.org/ce/z/ZfVrjD

umax(usub.sat(X, Y), X) --> X

• https://alive2.llvm.org/ce/z/ec8xDQ

umin(usub.sat(X, Y), X) --> usub.sat(X, Y)

• https://alive2.llvm.org/ce/z/FLkAcA

[nikic]

I believe this is taking the wrong approach to these folds. What you want to implement is simplification for something like this: https://alive2.llvm.org/ce/z/f_Eg7U And then min/max simplification should fall out of that for free.