[InstCombine] Add support for max(a,b) + min(a,b) => a + b.

[InstCombine] Add support for max(a,b) + min(a,b) => a + b.

The same optimization for
  max(a,b) * min(a,b) => a * b
is added.

Correctness check:
uadd: https://alive2.llvm.org/ce/z/2rXDek
sadd: https://alive2.llvm.org/ce/z/zNu_er
uadd + nuw/nsw: https://alive2.llvm.org/ce/z/EaiNjB
sadd + nuw/nsw: https://alive2.llvm.org/ce/z/w_2Nrs

umul: https://alive2.llvm.org/ce/z/dgXRLr
smul: https://alive2.llvm.org/ce/z/hBjGzz
umul + nuw/nsw: https://alive2.llvm.org/ce/z/EaiNjB
smul + nuw/nsw: https://alive2.llvm.org/ce/z/87MNeS

Reviewed By: goldstein.w.n
Differential Revision: https://reviews.llvm.org/D147296